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A 

BRIEF  PRACTICAL  TREATISE 


ON 


MORTARS: 


AN  ACCOUNT  OF  THE  PROCESSES  EMPLOYED 


PUBLIC  WORKS  IN  BOSTON  HARBOR. 


BY 

LIEUT.  WILLIAM  H.  WRIGHT, 

UNITED    STATES    CORPS    OF    ENGINEERS. 


BOSTON: 
WILLIAM    D.  TICKNOR   &   COMPANY, 

MDCCCXLV. 


Entered  according  to  Act  of  Congress,  in  the  year  1845,  by 

William  H.  Wright, 

in  the  Clerk's  Office  of  the  District  Court  of  the  District  of  Massachusetts. 


BOSTON: 

PRINTED  BY  THURSTON,  TORRY  &.  CO. 

31  Devonshire  Street. 


PREFACE. 


Many  able  works  have  been  written  on  the  subject 
of  mortars.  But  no  one  of  those,  with  which  I  am 
acquainted,  contains  enough  of  detail  to  afford  much 
assistance  to  inexperienced  constructors ;  and  they 
are,  in  general,  so  voluminous,  and  withal  so  badly 
arranged,  that  the  information  which  they  contain  can 
only  be  acquired  after  laborious  research.  The  neces- 
sary consequence  follows,  that  few  read  them,  and 
the  composition  of  mortars,  upon  which  the  stability 
of  structures  so  «much  depends,  is  in  most  cases  left 
entirely  to  the  judgment  of  uninformed  workmen. 
Such  a  system  must  obviously  lead  to  the  worst  prac- 
tical results,  and  indicates  an  absolute  necessity  for 
some  new  effort  upon  a  subject  so  important. 

At  the  request  of  the  Chief  Engineer,  and  with  the 
hope  of  inducing  constructors  to  bestow  some  personal 


IV  PREFACE. 

attention  upon  the  mortars  which  they  employ,  these 
pages  have  been  drawn  up.  They  embrace  every- 
thing of  practical  interest  that  I  could  obtain  from  the 
existing  treatises  at  my  command,  as  well  as  the  re- 
sults of  my  own  experience  at  Fort  Warren,  Boston 
Harbor,  while  acting  as  the  assistant  to  Col.  Thayer, 
of  the  Corps  of  Engineers,  United  States  Army. 


For  the  drawings  accompanying  the  text,  I  am  indebted  to 
Lieut.  H.  L.  Eustis,  of  the  United  States  Corps  of  Engineers. 

Boston,  May,  1845. 


TABLE    OF   CONTENTS. 


CHAPTER  I. 


Calcareous  minerals,  and  the  limes  which  they  furnish.  —  Lime, 
whence  and  how  obtained.  —  Limestones,  how  distinguished.  — 
General  properties  of  lime.  —  Classification  of  limes  into  fat 
limes,  poor  limes,  hydraulic  limes,  and  hydraulic  cements. — 
Characteristics  of  these  different  limes.  —  Relation  between  the 
qualities  of  the  limes  and  the  chemical  constitution  of  the  stones 
whence  they  are  derived.  —  Magnesian  limestones.  —  Carbonate 
of  magnesia.  —  Plaster  of  Paris,  or  sulphate  of  lime,         .        .        1-14 


CHAPTER  II. 

The  various  materials  employed  in  the  preparation  of  mortars.  — 
Comprised  under  three  heads,  to  wit,  the  limes,  the  sands,  and 
the  pouzzolanas.  —  Poor  lime.  —  Fat  lime.  —  Hydraulic  lime.  — 
Slaking  of  lime,  three  modes  of,  with  remarks  upon  each.  — 
Hydraulic  cement.  —  Sands.  —  Classification  of  sands. — Mode 
of  clearing  sands.  —  Use  of  sand  in  mortars.  —  Pouzzolanas, 
classification  of,  into  natural  and  artificial.  — Pouzzolana  prop- 
er. —  Trass  or  terras.  —  The  Arenes.  —  Clays,  how  examined.  — 
Brick  or  tile  dust.  — Forge  scales  and  minion.  —  Slag  from  the 
iron  foundries, 14-38 


VI  CONTENTS. 


CHAPTER  III. 

Pages. 

On  the  general  composition  of  mortars.  —  General  principle.  — 
Modes  of  measuring  void  spaces  in  sands.  —  Economy  of  using 
mixed  sands.  —  Mode  of  determining  proportions  when  mixed 
sands  are  used.  —  Minimum  of  cementing  matter  in  mortars.  — 
Reasons  for  increasing  this  in  practice.  —  Rule  in  using  pouzzo- 
lanas.  —  Rule  in  preparing  mortar  for  masonry  in  general. — 
Table  of  twenty  different  compositions  used  by  Smeaton  in  the 
construction  of  the  Eddystone  lighthouse,  and  other  works,        .      38-52 

CHAPTER   IV. 

On  the  resistance  of  mortars.  —  Considered  under  four  points  of 
view.  —  Comparative  strength  determined,  by  breaking  with 
weights,  prisms  of  the  different  mortars.  —  Apparatus  used  for 
the  purpose,  described.  — Modes  of  testing  the  adhesiveness  of 
mortars.  —  Cohesive  strength  of  pure  hydraulic  cement,  illus- 
trated. —  Brunei's  experimental  semi-arches  described.  —  Mode 
of  determining  the  comparative  hardness  of  mortars,  .         .       52-61 


CHAPTER   V. 

On  the  fabrication  of  limes,  &c.  in  the  large  way.  —  Kilns  for 
burning  lime,  divided  into  two  classes.  —  Various  kinds  of  kilns 
described.  —  Combination  of  coke  oven  with  lime  kiln.  —  Man- 
agement of  the  burning.  —  Mode  of  mauufacturing  hydraulic 
cement.  —  Mode  of  restoring  its  qualities  when  damaged. — 
Manufacture  of  artificial  cement.  —  Manufacture  of  artificial 
pouzzolana, 61-78 

CHAPTER  VI. 

On  the  preparation  and  application  of  various  kinds  of  mortars.  — 
Mortars  classified.  —  Ingredients  of  mortars  and  mode  of  mea- 
suring them  employed  at  Fort  Warren.  —  Mortar  for  pointing, 
its  mode  of  preparation  and  application.  — Mortars  for  interior 
and  exterior  stucco,  how  prepared  and  applied.  —  Ordinary  mor- 
tars (fat  lime  and  sand).  —  Implements  used  at  Fort  Warren  in 
making  mortar.  —  Mortar-mill,  with  its  appendages,  described.  — 
Mortars  for  stone  and  brick  masonry.  —  Manipulation  of  these 
mortars. 78-106 


CONTENTS.  Vll 


CHAPTER  VII. 


Pages. 


On  concrete  and  some  of  its  applications.  —  Mode  of  preparing 
concrete.  —  Various  kinds  of,  used  at  Fort  Warren  for  the  foun- 
dations and  superstructure  of  walls,  and  the  roofings  of  case- 
mates, described  in  detail.  —  Advantages  of  employing  concrete 
in  constructions, 106-128 


CHAPTER   VIII. 

Theory  of  the  solidification  of  mortars, 128-141 

Index, 141-148 


A.MV  Farlan. 


TREATISE  ON  MORTARS. 


CHAPTER    I. 

CALCAREOUS    MINERALS,   AND    THE   LIMES    WHICH 
THEY  FURNISH. 

1.  The  material  from  which  lime  is  usually  ciaIbocate 

,    .  ,  *  , .  .         i      ol  ,,me'  un 

extracted,  is  a  carbonate   of   June,  or,  in  other  abundant 

words,  a  chemical  compound,  the  essential  com- ""  !iuactpr° 

ponents  of  which  are   lime   and  carbonic  acid. 

This  substance  is  widely  diffused  in  nature,  and 

exhibits  so  many  varieties  of  form  and  structure, 

that  it  would  be  scarcely  possible  to  enumerate 

them  all. 

2.  The  calcination  of  each  variety  of  lime-  o™  species 
stone  furnishes  a  different  product,  with  proper-  h6w™ob- 
ties  peculiar  to  itself.     Yet,  in  truth,  there  is  but    la'no<1' 
one  species  of  lime  (the  protoxide  of  calcium), 

that  which  is  obtained  by  calcining  pure  white 
marble.  All  the  other  products,  called  heretofore 
meager  lime,  hydraulic  lime,  &.C.,  are  only  nat- 
ural mixtures  of  lime  and  sand  or  crude  earth, 
existing  originally  with  water  and  carbonic  acid 
in  the  impure  limestone.* 

3.  Lime  is  obtained  principally  from  calca-  substances 
reous  minerals,  but  there  are  some  localities,  limas." 
where  it  is  procured  from  marine  deposits,  oyster 

*  Raucourt  sur  les  Mortiers,  page  2. 
1 


&  TREATISE    ON    MORTARS. 

shells,  madrepores,  animal  products ;  these,  how- 
ever, are  rare  cases.  * 
Mode  of       4.  Minerals    of  the    calcareous    class    always 

'in?n?ime-  dissolve,  either  wholly  or  in  part,  in  weak  acids, 
sumes.    ^y.jj.jj  more  or  less  brisk  effervescence,  and  may 
be  scratched  with  an  iron  point,  f 

They  are  sometimes  found  pure,  in  the  form 
of  calcareous  spar  and  white  marble,  but  more 
usually  contain  oxide  of  iron,  and  sometimes  a 
certain  quantity  of  sand,  alumina,  magnesia, 
oxide  of  manganese,  &c.  % 

Pure  lime.  5.  An  analysis  of  white  marble  by  Gen. 
Treussart  gave  for  its  component  elements  — 
carbonic  acid,  33;  lime,  64;  water,  3.  If  a 
portion  of  this  mineral  be  reduced  to  powder, 
and  heated  to  whiteness  in  an  open  crucible,  the 
carbonic  acid  and  water  which  it  contains  are 
driven  off,  and  lime  remains  in  a  pure  state.  It 
is  then  in  the  condition  of  quick  or  unslaked 
lime,  with  a  specific  gravity  of  2.3.  § 

Slaking  de-  6.  If  pure  lime,  immediately  after  being  cal- 
cined, is  mingled  with  a  proper  quantity  of  wa- 
ter, a  large  amount  of  hot  vapor  is  evolved,  and 
the  lime  is  reduced  to  a  thick,  clayey  paste, 
equal  in  bulk  to  more  than  three  and  a  half 
times  its  original  volume.  ||  The  lime  is  thus 
brought  to  a  thorough  state  of  division  by  the 
addition  of  water  (with  which  it  enters  into 
chemical  combination),  and  is  now  said  to  be 
slaked. 

Properties  7.  Pure  quick  lime  has  a  great  avidity  for 
water,  imbibing  it  rapidly  from  the  air,  and 
forming  with  it  a  chemical  compound,  termed 
hydrate  of  lime.     This  compound  contains  about 

*  Raucourt,  pacre  121.  t  Smith's  Vicat,  page  1. 

t  Totten's  Treussart,  page  2. 

§  Ibid,  page  1.  ||  Raucourt,  page  1C. 


lined. 


of  lime. 


LIMESTONES    AND    THEIR    LIMES.  5 

twenty-eight  parts  by  weight  of  lime  to  nine 
of  water,  and  is  always  formed  during  the  pro- 
cess of  slaking,*  though  the  lime,  in  acquiring 
a.  pasty  consistence,  absorbs  a  much  larger  quan- 
tity of  water.  In  truth,  if  it  be  pure,  and  is 
supplied  with  water  as  soon  as  it  comes  from 
the  kiln,  it  will  absorb  three  and  a  half  times 
its  weight  —  a  property  peculiar  to  lime,  and 
serving  to  distinguish  it  from  other  earths,  f 

Pure  quick  lime,  when  converted  into  paste 
by  the  addition  of  water,  will  retain  its  soft 
consistence,  as  long  as  it  is  kept  damp.  It  is, 
however,  dissolved  very  sparingly  by  water, 
though  it  possesses  the  singular  property  of 
being  more  soluble  in  cold  than  in  hot  water.  J 

It  has  a  great  affinity  for  carbonic  acid,  at- 
tracting it  readily  from  the  atmosphere,  and  can 
only  be  preserved  pure  by  being  kept  in  close 
vessels. 

8.  In  the  preceding  remarks,  I  have  spoken  ciagsifica- 
of  pure  lime.      The   lime,   however,  which  is  tlfaM£i 
used  for  building  purposes,  is  rarely  in  this  state, 

but,  besides  water  and  carbonic  acid  imbibed 
from  the  atmosphere,  contains  usually  some  of 
the  foreign  substances  mentioned  in  Article  4. 
These  substances  modify  the  properties  of  pure 
lime,  and,  when  combined  with  it  in  certain 
proportions,  entirely  change  its  nature.  It  will 
therefore  be  convenient  to  arrange  the  limes 
employed  in  constructions  into  four  different 
classes:  1st.  The  fat  or  common  limes;  2d. 
The  poor  or  meager  limes ;  3d.  The  hydraulic 
limes ;  and,  4th.  The  hydraulic  cements. 

9.  The  fat  or  common  limes  are  more  than  Fatiimc*. 
doubled  in  volume  during  the  process  of  slaking, 

*  Capt.  Smith's  Vicat,  pasje  34.  t  Raucourt,  page  2. 

$  Turner's  Chemistry,  page  311. 


4  TREATISE    ON    MORTARS. 

which  is  always  attended  with  much  heat.  If 
converted  into  paste  and  immersed  in  water, 
they  will  remain  of  soft  consistence  forever ; 
and  they  are  soluble  to  the  last  particle  in  pure 
water,  if  it  be  frequently  changed.*  Builders 
call  them  fat  limes,  because  the  paste,  which 
they  form  with  water,  is  soft  and  unctuous  to 
the  touch. 

Poor  iimc?.  10.  The  poor  or  meager  limes  include  all 
those  which,  in  slaking,  do  not  undergo  an  in- 
crease of  volume  equal  to  twice  their  original 
bulk,  but  exhibit,  when  immersed,  the  same 
qualities  as  the  rich  limes,  with  this  difference, 
that  they  dissolve  more  partially  in  water,  leav- 
ing usually  a  large  residue  of  insoluble  matter,  f 

Hy.irauiic  1 1.  The  hydraulic  limes  possess  the  property 
iimes.  0£  sefijng  iin(ier  water,  in  periods  of  time  vary- 
ing from  one  to  forty  days  after  immersion,  and 
continue  to  harden  more  or  less  rapidly,  accord- 
ing to  the  hydraulic  energy  which  they  respect- 
ively possess.  They  all  slake,  but  with  diffi- 
culty ;  the  stronger  kinds  exhibiting  few  or  none 
of  the  appearances  usually  seen  in  fat  lime 
during  the  slaking  process,  little  or  no  vapor 
being  formed,  and  scarcely  any  heat  disengaged  ; 
and  they  undergo  an  increase  of  volume,  in  the 
inverse  ratio  of  their  hydraulic  energy. f 

Hydraulic  12.  The  hydraulic  cements  differ  from  the 
limes,  in  not  slaking  at  all  after  calcination, 
unless  they  are  previously  pulverized  ;  and  they 
then  form  a  paste  with  water,  without  any  per- 
ceptible disengagement  of  heat,  or  augmenta- 
tion of  volume.  They  contain  a  large  amount 
of  the  hydraulic  base  or  principle,  and  set  under 
water  in  a  much  shorter  time  than  the  limes 
require  to  set  in  air. 

*  Smith's  Vicat,  page  6.  t  Ibid,  pages  6,  7. 


LIMESTONES    AND    THEIR    LIMES.  i 

13.  In  the  preceding  articles,  the  term  setting  Setting  <ie 
has  been  employed ;  and,  as  no  precise  idea  may 
be  attached  to  it,  I  will  fix  rigorously  its  mean- 
ing, by  assuming  some  definite  period,  at  which 
it  is  supposed  to  take  place.  In  every  case,  the 
lime  or  mortar  may  be  regarded  as  having  set, 
when  its  consistence  has  become  firm  enough 
to  support,  without  depression,  a  wire  with  a 
diameter  of  one  twenty-fourth  part  of  an  inch, 
and  loaded  to  weigh  one  pound.* 


EXAMINATION    OF    LIMESTONES. 

14.  The  situation  in  which  the  mineral  may   physical 
be  found,  its  texture,  its  color,  its  hardness,  its  no'guUte! 
weight,  and  all  the  other  rules  with  which  the 
books  have  been  filled  since  the  time  of  Vitru- 

vius,  afford  no  certain  means  of  discovering  the 
kind  of  lime  which  it  will  furnish.  Even  chem- 
ical analysis,  which  is  not  within  the  reach  of 
every  one,  is  but  an  approximate  guide.  Actual 
trial  by  experiment  is  alone  to  be  relied  upon.f 

15.  The  first  thing  to  be  done  with  a  mineral  Mo,,!!  of 

...  .  r  testing 

under  examination,  is  to  pulverize  a  few  ounces,  limestone. 

and  then,  placing  the  powder  in  a  glass  retort, 

to  add  nitric,  hydrochloric,  or  sulphuric    acids. 

If  the  gas,  made  to  pass  through  lime-water  as 

it  comes  from  the  beak  of  the  retort,  renders  the 

lime-water  opaque,  the  substance  is  a  carbonate 

of  lime.      Having  ascertained  that  it  is  a  car- 


bonate, proceed,  in  the  next  place,  to  discover 
if  it  be  a  pure  carbonate  of  lime,  or  the  kind 
of  lime  which  it  will  afford  by  calcination. 
With  this  view,  break  the  stone  into  pieces  of 

*  Totten  on  Mortars,  page  229. 

t  Raucourt,  page  122. — Smith's  Vicat,  page  3. 

1* 


O  TREATISE    OX    MORTARS. 

the  size  of  an  egg,  and  expose  it  in  a  common 
fireplace,  if  no  furnace  be  at  hand,  to  a  strong 
red  heat,  for  about  three  hours.  The  mineral 
will  probably  be  sufficiently  burned  in  that  time  ; 
but,  in  order  to  be  sure  of  this,  slake  a  portion 
of  the  calcined  stone,  and  pour  upon  it  one  of 
the  acids  before  mentioned ;  if  the  calcination 
has  been  complete, — that  is,  if  all  the  carbonic 
acid  has  been  driven  off,  —  there  will  be  no 
effervescence.* 

r-oor  lime.  16.  Should  the  slaking,  after  some  little  de- 
lay, take  place  with  the  usual  energy,  while  the 
lime  increases  but  little  in  volume,  and  is  only 
partially  dissolved  by  the  acid,  an  insoluble  resi- 
due being  left  behind,  the  substance  under  ex- 
amination may  be  classed  as  a  poor  lime  ;  its 
meager  qualities  being  in  proportion  to  the 
amount  of  foreign  matter  left  undissolved.! 

The  proportion  of  these  granular  substances, 
as  compared  with  that  of  the  lime,  should  al- 
ways be  carefully  ascertained,  as  it  regulates  the 
quantity  of  sand  that  may  be  used  in  making 
mortar,  whenever  necessity  requires  the  employ- 
ment of  meager  limes,  J  in  general  proscribed. 
The  mode  of  measuring  them  is  explained  in 
Article  21. 

rut  limes.  17.  If  the  slaking  be  effected  immediately, 
and  with  violence,  and  much  hot  vapor  is  dis- 
engaged, while  the  resulting  paste  equals  in  bulk 
from  two  to  three  times  the  original  volume  of 
the  lime,  the  specimen  under  trial  may  be  re- 
ferred to  the  class  of  fat  limes,  its  fatness  being 
proportional  to  the  increase  in  bulk,  f 

Hyhiuiic       18.   Should  there  be  little  heat  disengaged,  or 
iin';j'     water  absorbed,  during  the  slaking  process,  and 

*  Gen.  Pasley,  page  31.  +  Vicat.  page  6. 

*  Raucourt,  page  52. 


LIMESTONES    AND    THEIR    LIMES.  7 

the  lime  acquire  but  a  small  increase  of  volume, 
it  is  probably  a  hydraulic  lime.  To  examine  its 
character  more  particularly,  convert  a  portion  of 
it  into  stiff  paste,  making  use  of  bibulous  paper 
to  absorb  any  excess  of  water,  until  it  will 
support,  without  sensible  depression,  a  wire  one- 
twelfth  of  an  inch  in  diameter,  and  loaded  with 
one  quarter  of  a  pound.*  Noting  accurately  the 
time,  place  the  paste  thus  prepared  in  the  bottom 
of  a  tumbler,  and,  pressing  down  its  surface  to 
a  level,  cover  it  immediately  with  water.  Ob- 
serve it  closely,  and,  if  any  cracks  manifest 
themselves  upon  the  surface, — which  would 
usually  be  the  case  with  hydraulic  limes, — pour 
off  the  water,  work  the  paste  over  again  thor- 
oughly, and,  having  allowed  it  to  become  stiff 
as  before,  cover  it  a  second  time  with  water,  and 
repeat  this  operation  until  cracks  no  longer  ap- 
pear. If  it  sets  in  one  or  two  days,  it  is  an 
eminently  hydraulic  lime ;  if  it  requires  fifteen 
or  twenty  days  for  this  purpose,  it  is  only  mod- 
erately hydraulic ;  and,  should  it  remain  soft 
after  some  forty  days  have  elapsed,  it  must  be 
regarded  as  belonging  to  one  of  the  first  two 
classes  of  limes,  which  possess  no  hydraulic 
properties.! 

19.  If  the  calcined  mineral  does  not  slake  at  Hydraulic 
all,  reduce  a  fragment  of  the  stone  to  an  im- 
palpable powder,  by  grinding  or  pounding  in  a 
mortar.  The  fineness  of  the  powder  may  be 
ascertained  by  rubbing  a  pinch  between  the 
finger  and  the  thumb  ;  if  it  feels  gritty,  continue 
to  pulverize  it  until  the  grittiness  is  no  longer 
perceptible.  Then  make  a  portion  of  the  pow- 
der into  a  cake  or  ball  with  water,  of  such  a 

*  Totten  on  Mortars,  page  220. 

t  Smith's  Vicat. — Gen.  Pasley,  page  179. 


b  TREATISE     ON    MORTARS. 

size  as  to  lie  in  the  bottom  of  a  tumbler  without 
touching  the  sides,  and  immerse  it  as  recom- 
mended in  the  preceding  article.  Should  it  be 
a  hydraulic  cement  of  good  quality,  it  will  re- 
tain the  ball-like  form,  without  exhibiting  cracks 
upon  its  surface,  and,  if  exceedingly  hydraulic, 
will  set  instantly ;  if  but  slightly  so,  it  may 
require  three  or  four  days  to  become  hard.  A 
cement,  if  energetic,  however,  should  set  in  four 
to  six  minutes  after  immersion,  and  may  in  gen- 
eral be  regarded  as  good  in  proportion  to  the 
promptness  of  its  induration.  There  is  one 
important  caution  to  be  observed  in  regard  to 
the  above  test.  The  cake  should  be  allowed  to 
remain  immersed  for  a  day  or  two,  however 
quickly  it  may  have  set  in  the  first  instance. 
It  sometimes  happens  that  there  is  quick  lime 
present,  which  continues  to  slake,  and  breaks 
down  the  mass,  after  the  hydraulic  ingredients 
have  indurated.*  Should  this  take  place,  the 
substance  may  be  regarded  as  a  hydraulic  lime, 
and  should  then  be  treated  as  advised  in  Ar- 
ticle 18. 
Remarks.  20.  In  the  preceding  remarks,  I  have  supposed 
the  constructor  to  calcine  the  mineral,  though, 
more  usually,  the  limes  and  cements  which  he 
employs  are  manufactured  for  his  use  by  others. 
In  every  case,  however,  their  qualities  should  be 
tested  with  great  care,  before  they  are  employed 
as  ingredients  of  mortar. 
Berthier's  21.  M.  Berthier  proposes  a  method  of  ana- 
analysis!"  lyzing  limestones,  which  dispenses  with  the 
necessity  of  calcination.  His  process  is  to  pul- 
verize the  mineral,  and  pass  the  product  through 
a  hair  or  silk  sieve.     Upon  a  given  weight  ( 154.4 

*  Totten  on  Morlars,  page  229. 


LIMESTONES    AND    THEIR    LIMES. 

grains)  of  the  powder  thus  obtained,  lie  then 
pours  muriatic  acid  (or,  in  case  he  has  no  muri- 
atic, nitric  acid  or  vinegar),  slightly  diluted  with 
water,  stirring  it  continually  with  a  glass  or 
wooden  rod.  As  soon  as  the  effervescence  ceases, 
he  discontinues  adding  the  acid,  and  then  evap- 
orates the  solution  by  a  gentle  heat  to  the  con- 
sistence of  paste.  About  a  pint  of  water  is  now 
poured  upon  the  mass,  and  the  whole  is  passed 
through  a  paper  filter  by  means  of  a  funnel. 
The  clay  remains  suspended  on  the  filter,  is 
carefully  dried  and  weighed,  or,  better  still,  may 
be  heated  to  redness  in  an  earthen  or  metal 
crucible,  previous  to  being  weighed. 

Very  clear  lime-water  is  now  added  to  the 
solution  as  long  as  a  precipitate  is  formed.  This 
precipitate,  which  is  magnesia,  sometimes  mixed 
with  iron  or  manganese,  is  collected  as  soon  as 
possible  on  a  filter,  washed  in  pure  water,  dried 
at  a  high  heat,  and  finally  weighed.  The  weight 
of  the  clay,  compared  with  that  of  the  mineral, 
gives  an  approximate  indication  of  its  hydraulic 
character.  But  it  might  happen  that  the  sub- 
stance remaining  suspended  after  the  first  filtra- 
tion may  consist  entirely  of  sand,  or  of  sand 
mixed  with  clay.  In  the  first  case,  the  mineral 
will  afford  nothing  more  than  a  poor  lime,  and 
the  sandy  particles  should  be  carefully  measured 
and  weighed  ;  #  in  the  second,  the  sand  and  clay 
should  be  separated  by  washing  and  decantation, 
and  the  weight  of  each  ascertained  separately,  f 

22.  A  chemical  examination  of  calcareous 
minerals  would  show,  in  a  general  way,  the 
following  ingredients,  in  addition  to  the  carbon- 
ate of  lime  : — 


*  See  Article  16. 

+  Totten  on  Mortars,  page  13. — Smith's  Vicat,  page  1 13. 


10  TREATISE    ON    MORTARS. 

chemical  1st.  Ill  those  furnishing  the  poor  limes,  silica 
"of  poor    in  the  state  of  sand,  magnesia,  oxide  of  iron  and 

hmes"  manganese  in  variable  proportions,  not  exceeding 
.30  of  the  whole.* 

or  rich        2d.  In  such  as  yield  the  rich  limes,  from  .01 

limes*  . 

to  .06  of  silica,  alumina,  magnesia,  iron,  &c, 
existing  separately,  or  two  and  two,  three  and 
three,  &c* 

of  hydrau-  3d.  In  those  affording  the  hydraulic  limes, 
silica,  alumina,  magnesia,  iron,  and  manganese, 
in  different  relative  proportions,  but  usually  not 
exceeding  .25  of  the  whole,  the  silica  generally 
predominating  in  the  stronger  limes.* 

or  hydrau-      4th.  In   the   cement   stones,  sometimes  mag- 

lic  cements.  .         .  1  j        i.       •  l 

nesia,  iron,  manganese,  potash,  soda,  besides  an 
amount  of  clay  varying  from  twenty  per  cent,  to 
more  than  one  half  of  the  whole  weight  of  the 
mineral  examined.f 
Dolomites.  23.  The  double  carbonates  of  lime  and  mag- 
nesia, called  dolomites,  afford  a  lime  which  is 
capable  of  setting  under  water.  They  are  en- 
tirely soluble  in  dilute  acids,  but  do  not  slake 
at  all,  or  very  imperfectly,  if  the  mineral  contains 
a  large  proportion  of  magnesia,  this  substance 
not,  combining  with  water  until  after  exposure 
for  some  time  to  its  action.  | 
Mode  of       24.   On  the  above-mentioned  property  of  maa:- 

analyzing  .  „  ,      -.  iii-1  •• 

them,  nesia  has  been  founded  a  method  ol  determining 
the  respective  quantities  of  lime  and  magnesia, 
which  a  magnesian  limestone  may  contain.  It 
is  Mr.  Prinsep's  process,  and  consists  in  reducing 
the  mineral  to  powder  and  then  exposing  it  to 
strong  heat,  until  all  the  carbonic  acid  is  driven 
off.  If  it  were  a  carbonate  of  lime  only,  the 
quantity  of  carbonic  acid  expelled  would  be  §§ 

*  Vicat,  page  9.  t  Totten  on  Mortars,  page  181. 

%  Vicat,  page  8. 


LIMESTONES    AND    THEIR    LIMES.  11 

of  its  weight,  the  remaining  §§■  being  pure  lime. 
The  lime  being  then  converted  into  a  hydrate 
by  the  addition  of  water,  would  gain  an  increase 
of  -2S  of  its  weight.  *  Hence,  to  obtain  the 
quantity  of  pure  lime  in  a  double  carbonate  of 
lime  and  magnesia,  it  is  only  necessary  to  mul- 
tiply the  increase  of  weight  after  slaking  by  2F8 
(or  3£)  ;  and  the  same  increase  of  weight,  mul- 
tiplied by  5g-,  will  give  the  corresponding  quan- 
tity of  carbonate  of  lime,  which  existed  in  the 
mineral  previous  to  calcination.  The  remainder 
will  be  carbonate  of  magnesia,  unless  there 
should  be  silex,  or  any  of  the  insoluble  earths, 
united  to  the  double  carbonate.  In  that  case, 
the  respective  amounts  of  these  foreign  matters 
should  be  previously  ascertained,  by  solution  in 
an  acid  and  decantation.  In  carbonate  of  mag- 
nesia, nearly  47  per  cent,  is  magnesia,  and  the 
remaining  53  carbonic  acid.f 

25.  Though  not  comprised  among  limestones,  catbonat 
the  native  carbonate  of  magnesia  may  here  be  °ne?iaf 
mentioned  as  furnishing  a  cement,  which  is  used 
to  some  extent  in  India,  for  building  purposes. 
This  mineral  dissolves  readily  in  muriatic  acid, 
and  may  be  distinguished  from  the  carbonate 
of  lime  by  yielding  a  precipitate  of  magnesia, 
when  lime-water  is  added  to  the  solution.  After 
calcination,  the  magnesia  does  not  slake,  but, 
upon  being  pulverized  and  formed  into  a  paste 
with  water,  gives  off  a  sensible  amount  of  heat. 
It  acquires  in  time  a  firm  consistency,  and  has 
the  property  of  hardening  under  water,  though, 
previous  to  immersion,  it  should  be  allowed  to 
dry  in  the  air,  for  twelve  hours  or  more.  Like 
the  hydraulic  limes,  its  properties  are  impaired, 

*  See  Article  7.  t  Smith's  Vicat,  page  146. 


12  TREATISE    ON    MORTARS. 

after    calcination,    by   exposure    to    the    atmo- 
sphere.* 

Gypsum.  26.  Gypsum,  or  plaster-stone,  the  mineral 
which  supplies  the  plaster  for  cornices,  orna- 
mental ceilings,  and  the  like,  being  a  sulphate, 
not  a  carbonate,  of  lime,  is  also  not  usually 
embraced  in  the  class  of  limestones.  "When 
pure,  however,  it  is  not  unlike  white  marble, 
and  is  then  known,  commonly,  under  the  name 
of  alabaster.  In  the  calcined  state,  it  is  gene- 
rally called  plaster  of  Farts,  for  the  reason  that 
the  mineral  is  found  in  great  abundance  near 
the  French  capital,  f 
Howdigtio-  27.  Gypsum  is  distinguished  from  the  carbon- 
ate of  lime,  by  not  effervescing  nor  undergoing 
any  change  in  dilute  acids,  and  by  not  slaking 
at  all,  nor  forming  a  plaster  fit  for  use,  when 
burned  in  the  usual  way  in  which  limestone  is 
calcined. f 

Mode  of  28.  Its  quality  may  be  ascertained  practically 
tequaifty!5  hy  the  following  process.  Pulverize  a  fragment 
of  the  stone,  and,  placing  the  powder  in  a  shal- 
low dish  of  tin  or  iron  over  a  brisk  fire,  stir  it 
continually.  In  a  short  time,  the  water  which 
it  contains  will  be  driven  off  with  much  violence, 
in  the  form  of  steam.  As  soon  as  the  disen- 
gagement of  steam  is  no  longer  perceptible, 
invert  a  dry  wine-glass  over  the  powder,  and, 
if  the  inside  of  the  glass  present  no  appearance 
of  moisture,  the  powder  is  then  sufficiently 
burned.  A  small  portion  of  it,  kneaded  into  a 
cake  with  water,  should  set  with  moderate  heat, 
forming  a  very  hard  white  substance  ;  and  it 
will  even  continue  to  harden  under  water,  but, 


*  Smith's  Vicat,  page  147. 

t  Pasley  on  Cements,  pages  10,  11. 


LIMESTONES    AND    THEIR    LIMES.  13 

being  partially  soluble,  is  not  applicable  to  hy- 
draulic constructions.* 

29.  The  process  described  in  the   preceding  Modes  of 
article  is  often  employed  in   preparing   gypsum Pmh?i^ 
for  use  in  the  large  way ;  and  another  common        y" 
method  is,  to  break  the  stone  into  small  pieces, 
bake  it  in  an  oven,  and  afterwards  grind  it  to 
powder.     The  plaster,  prepared  in  either  way, 
imbibes   moisture    if   exposed    to    the   air,    and 
would  soon  be  entirely  spoiled,  unless  kept  in 
air-tight  casks  or  sacks,  as  is  generally  the  case 
with  that  on  sale.     When  its  qualities  are  in- 
jured by  absorbing  moisture,  they  may  be  re- 
stored by  burning  it  again.* 

*  Pasley,  pages  11,  12. 


14  TREATISE    ON    MORTARS. 


CHAPTER    II. 

THE  VARIOUS  MATERIALS  EMPLOYED  IN  THE 
PREPARATION  OF  MORTARS. 

ingredients      30.  These  materials  may  be  comprised  under 

of  mortar.    . ,  ,  n  •*• 

three  heads : 

1st.  The  limes. 

2d.  The  different  kinds  of  sand,  properly  so 
called. 

3d.  The  pouzzolanas,  both  natural  and  artifi- 
cial. 

THE    LIMES. 

Remarks  on  31.  The  limes  were  divided  (article  8),  into 
3'  four  classes,  viz.  the  Poor  Limes,  the  Fat  Limes, 
the  Hydraulic  Limes,  and  the  Hydraulic  Ce- 
ments. The  first  should  never  be  used,  except  in 
case  of  absolute  necessity.  Besides  being  en- 
tirely devoid,  like  the  fat  limes,  of  hydraulic 
energy,  they  are  usually  mingled  with  a  large 
amount  of  inert  matter,  and  acquire  little  or  no 
increase  of  bulk  in  slaking.  My  remarks  will 
therefore  be  directed  to  fat  lime,  hydraulic  lime, 
and  hydraulic  cement ;  and  in  the  first  place  to 
the  two  former  of  these. 

Fat  or  common  lime,  in  consequence  of  its 
great  consumption  for  building  purposes,  is  now 
an  article  of  commerce  in  all  the  cities  of  the 
country,  and  its  manufacture  has  become  an  im- 
portant and  distinct  branch  of  the  useful  arts. 
It  is  prepared  on  the  largest  scale  in  the  State  of 
Maine,  and  the  kilns  of  Thomaston  and  the 
neighboring  villages  furnish  it  in  great  abun- 
dance, at  very  cheap  rates  and  of  most  excellent 


INGREDIENTS     OF    MORTARS.  15 

quality.  At,  the  public  works  in  Boston  Harbor, 
the  Thomaston  lime  has  been  generally  pre- 
ferred, as  it  combines  lowness  of  price  with  a  con- 
siderable degree  of  richness.  It  slakes  promptly, 
and  yields,  in  stiff  paste,  a  volume  of  eight  cu- 
bic feet  for  each  cask  of  240  pounds. 

Hydraulic  limestones  (as  distinguished  from 
cement  stones)  exist  in  great  abundance  in  this 
country,  though,  I  believe,  they  are  nowhere 
calcined  with  a  view  to  sale  in  the  large  way. 
The  limes  which  they  yield  form  the  intermedi- 
ate class  between  the  common  limes  and  the 
hydraulic  cements,  and  fill  up  all  the  gradations 
between  the  inert  character  of  the  one  and  the 
exceeding  energy  of  the  other. 

Both  fat  and  hydraulic  limes  should  be  kept 
in  tight  casks  and  in  a  dry  room,  so  as  to 
be  sheltered  as  well  as  possible  from  the  action 
of  the  atmosphere.  It  is  economical  to.  use  them 
as  soon  as  possible  after  calcination,  for  if  ex- 
posed for  any  length  of  time  in  the  casks,  which 
soon  become  loose  on  account  of  the  drying  ac- 
tion of  the  lime,  they  slake  with  difficulty,  and 
the  resulting  volume  of  paste  is  greatly  dimin- 
ished, while  the  energy  of  the  hydraulic  varie- 
ties is  at  the  same  time  much  impaired. 

32.  As  lime  comes  from  the  kiln  in  the  condi-Fir.3t,  ™od8 
tion  oi  quick  lime,  it  is  necessary  to  slake  it,  be-  Hme. 
fore  it  can  be  employed  in  the  preparation  of 
mortars.  There  are  three  modes  of  doing  this. 
The  first  consists  in  throwing  upon  it  sufficient 
water  to  reduce  it  to  a  thick  pulp.  This  is  the 
ordinary  method,  but  it  is  generally  abused  by 
pouring  so  much  water  upon  the  lime  as  to 
drown  it,  or  in  other  words  to  form  a  thin  cream, 
and  thus  impair  its  binding  qualities. 

One  volume   of  fat  lime,  slaked  in  the  above 


16 


TREATISE    ON    MORTARS. 


manner,  yields  from  two  to  three  and  a  half  vol- 
umes of  stiff  paste,  while  the  meager  limes  and 
the  more   energetic  hydraulic   limes  rarely  give 
more  than  one  and  a  half  volumes.* 
Mode  of  as-      33.   The  increase  of  bulk  in  slaking  is  easily 
increase'of  ascertained  by  filling  any  vessel  to  a  convenient 
volume,   height  with  the  lumps  of  quick  lime,  and  then 
pouring  in  dry  sand  until  the  vessel  is  entirely 
full.     The  sand  should  now  be  separated  from 
the  lime,  which  is  then  slaked  in  the  vessel  by 
itself.     When  the  slaking  is  over,  sand  is  again 
poured  in,  and  the  difference  between  the  quan- 
tity now  required  to  fill  the  vessel,  and  that  pre- 
viously used,  gives  at  once  a  measure   for  the 
augmentation  of  volume. f 
Precaution      34.   There  is  one  precaution  to  be  observed  in 
"ly'fitst8  employing    the    method    of    slaking,  above    de- 
method.   scribed.     Sufficient  water  to  produce  the  desired 
result  should  be  used  at  first ;  or  at  all   events, 
any  additional   quantity  that  may  be  requisite, 
should  be  supplied  very  gradually.     If  any  por- 
tion of  lime  is  permitted  to  slake  to  dryness,  and 
water  is  afterwards  thrown  suddenly  upon  it,  it 
appears  to  become  benumbed,  and  falls  to  pow- 
der very  imperfectly.^ 
siaWnf  by      35.   The  second  method  of  slaking  lime  con- 
immersion.  g-gts  m   piunging  it  into  water,  and  then  with- 
drawing it  after  a  few  seconds,  before  the  com- 
mencement of  ebullition.    The  lime  hisses,  bursts 
with  noise,  and  falls  into  fine  powder,  evolving 
hot  vapor  at  the  same  time.     It  is  then  said  to 
be    slaked    by    immersion.      The    powder    thus 
obtained,   does  not  again   become   heated  upon 
being  made  into  paste  with  water,  and  may  be 

*  Smith's  Vicat,  p.  26.  t  Raucourt,  p.  16. 

t  Smith's  Vicat,  pp.  27,  2S. 


INGREDIENTS    OF    MORTARS.  17 

preserved  for  a  long  time,  if  care  be  taken  to 
protect  it  from  the  atmosphere. 

Fat  lime  slaked  by  this  process  gives,  for 
each  volume  of  powdered  quick  lime,  one  and  a 
half  volumes  of  slaked  powder,  measured  with- 
out compression,  while  the  hydraulic  limes,  under 
similar  circumstances,  give  sometimes  more  than 
two  volumes.* 

36.  In  order  to  ensure  the  best  result  in  slak-  Precaution 

/■•it  to  be  o!)- 

ing  by  immersion,  the  fragments  of  quick  lime  servCu. 
should  be  reduced  in  the  first  place  to  the  size  of 
a  walnut,  and  heaped  together,  immediately  after 
they  are  withdrawn  from  the  water,  in  casks  or 
large  bins.  The  heat  is  thus  concentrated,  and 
a  large  amount  of  vapor,  which  would  otherwise 
escape,  is  absorbed  by  the  lime,  which  is  brought 
in  consequence  to  a  more  thorough  state  of  di- 
vision.! 

37.  Quick  lime,  abandoned  to  the  slow  and  Air  s,akinz- 
continued  action  of  the  atmosphere,  is  reduced 

in  process  of  time  to  a  fine  powder.  The  natu- 
ral or  spontaneous  slaking  thus  effected,  is  at- 
tended with  a  very  slight  disengagement  of  heat, 
but  with  no  sensible  emission  of  vapor. f 

This  third  method  of  extinction  was  formerly 
proscribed,  and  the  powder  resulting  from  it  re- 
garded as  worthless.  Recent  experiments  have 
shown,  however,  that  in  some  cases,  common  fat 
lime,  reduced  to  powder  by  spontaneous  slak- 
ing, and  stirred  from  time  to  time,  to  allow  the 
air  to  act  upon  every  part  of  it,  will  acquire,  af- 
ter a  year's  exposure,  the  hydraulic  property  of 
setting  under  water  ;  f  but  to  determine  whether 
this  result  be  universal,  is  still  a  subject  of  ex- 
periment. 

*  Smith's  Vicat,  pp.  27,  28.  t  Raucourt,  pp.  17,  13. 

2* 


IS 


TREATISE    ON    MORTARS. 


<  'lioico  of 
the  mode 
of  slakin». 


38.  The  choice  of  the  process  of  extinction 
depends  somewhat  upon  the  object  which  the 
constructor  has  in  view.  If  the  result  mention- 
ed in  the  preceding  article  be  proved  universal, 
the  third  method  (air  slaking),  should  be  used 
with  the  fat  limes,  when  it  is  desirable  to  in- 
crease their  binding  qualities  ;  the  first,  or  ordi- 
nary process,  with  the  eminently  hydraulic  limes; 
and  the  second,  or  that  by  immersion,  with  the 
limes  comprised  between  the  two  extremes.* 
The  ordinary  method  most  perfectly  divides  the 
fat  limes  and  the  hydraulic  limes  of  all  degrees, 
and  consequently  raises  their  expansion  to  the 
highest  limit.  The  difference  in  this  respect 
between  the  several  modes  of  extinction,  partic- 
ularly in  the  case  of  the  fat  limes,  is  exhibited 
in  the  following  table  extracted  from  Vicat's 
able  work  on  Mortars.f 


Water 

Hulk  of 

absorbed. 

paste. 

One  volume,  weighing  100  kilogrammes 
of  fat  lime,  converted  into  thin  paste  by  the 

Kil. 

Vol. 

first  process,  gives       ..... 

291 

3.50 

The  same,  previously  slaked  by  immer- 

172 

2.34 

The  same,  first  slaked  spontaneously     . 

188 

2.58 

One  volume,  weighing  100  kilogrammes, 

of  hydraulic    lime,  converted   into  a   thin 

paste  by  the  first  process,  gives 

105 

1.37 

The  same,  previously  slaked  by  immer- 

71 

1.27 

The  same,  first  slaked  spontaneously     . 

68 

1.00 

Note.  —  The  numbers  in  the  above  table  are 
comparative,  and  the  kilogramme,  for  this  reason, 
has  not  been  converted  into  its  equivalent  Eng- 
lish weight,  which  is  2  lbs  3  oz.  4.43  drachms 
avoirdupois,  or  more  conveniently  and  quite  near 
2  -&  lbs. 


*  Raucourt,  pp.  17,  13. 


t  Smith's  Vicat.p.  163. 


INGREDIENTS    OF    MORTARS.  19 

We  see  from  the  table,  that  both  fat  and  hy- 
draulic lime  yield  the  largest  volume  of  paste, 
when  slaked  by  the  ordinary  process.  The 
largest  quantity  of  mortar  may  therefore  be  ob- 
tained by  employing  this  method,  as  the  propor- 
tion of  sand  in  practice  is  always  regulated  by 
the  amount  of  paste.  It  must  therefore  be  re- 
garded as  the  most  economical,  even  if  each  of 
the  three  modes  of  extinction  involved  the  same 
cost  of  manipulation.  But  the  second  and  third 
are  more  expensive  in  this  respect  also ;  and  as 
they  have  in  general  no  other  object  than  to  de- 
velop a  little  more  of  hydraulic  energy  in  the 
weaker  limes,  we  can  produce  this  effect  always 
with  more  certainty,  and  usually  with  more 
economy,  by  the  addition  of  hydraulic  cement, 
or  some  of  the  other  products  to  be  hereafter  de- 
scribed.* The  method  first  explained  may  there- 
fore be  regarded  as  the  most  advantageous  in  al- 
most every  case. 

With  either  mode  of  slaking,  fresh  water,  as 
free  from  impurities  as  possible,  should  always 
be  preferred.  The  amount  of  resulting  paste  is 
greatly  diminished,  if  salt  water  be  employed  in 
slaking  the  lime. 

39.  Fat  lime,  slaked  by  the  ordinary  method,    M°deof 

.  .  .      ,       p     .  preserving 

may  be  preserved  for  an  indefinite  period  of  time,  rich  limes, 
by  placing  it  in  trenches  or  other  reservoirs,  and 
securing  it  from  the  action  of  the  atmosphere  by 
a  covering  of  sand  or  fresh  earth.  When  slaked 
by  immersion,  or  spontaneously,  it  may  be  kept 
without  change  for  a  tolerably  long  time,  either 
in  casks  or  under  sheds  in  large  bins,  covered 
with  cloths  or  straw.f 

40.  Hydraulic  limestone  is  calcined  with  diffi-  ^""j^" 

lime. 
*  Raucourt.  p.  15.  t  Vica*,  p.  32. 


20  TREATISE    ON    MORTARS. 

culty  to  the  proper  degree,  and  when  not  suffi- 
ciently burned,  the  resulting  lime  slakes  badly. 
The  mortar,  made  with  it  in  such  a  state,  is  less 
tenacious,  and  is  moreover  apt  to  swell  after 
being  used,  to  the  great  injury  of  the  masonry. 
To  ensure  thorough  slaking,  it  should  generally 
be  allowed,  after  extinction,  to  remain  twelve 
hours  or  more  before  it  is  employed,  but  it  is 
best  in  every  case  to  ascertain  approximately  the 
time  required  for  this  purpose,  by  experimenting 
in  a  small  way.  Hydraulic  lime  becomes  hard, 
however,  in  a  short  time  after  being  converted 
into  paste,  and  should  never  be  slaked  in  greater 
quantity  than  will  suffice  for  two  days'  consump- 
tion at  most.*  After  leaving  the  kiln,  it  soon 
loses  a  portion  of  its  energy,  if  exposed  to  the 
action  of  the  air,  and  finally  passes  to  the  state 
of  common  lime.  Notwithstanding  the  precau- 
tions required  in  its  use,  it  may  be  employed 
very  advantageously  when  of  good  quality  ;  as 
it  frequently  offers  the  only  means  of  making 
excellent  mortars,  at  a  cheap  rate.* 
Mode  of  41.  Hydraulic  lime,  if  previously  slaked  by 
preserving  immersion,   and  then  secured   in   the  powdered 

hydraulic  .  '  -  x  r 

lime,  state  in  casks,  or  sacks  of  cloth,  may  be  kept  for 
a  long  time  without  sensible  alteration.  The 
following  method  has,  however,  been  employed 
with  success,  in  preserving  a  considerable  quan- 
tity in  the  caustic  state  for  five  or  six  months. 
A  layer  of  the  lime,  reduced  to  powder  by  im- 
mersion, about  seven  inches  thick,  is  first  spread 
upon  the  floor  of  the  shed  or  room  in  which  the 
mass  is  to  be  kept.  On  this  layer,  the  quick 
lime,  packed  as  closely  as  possible,  is  then  piled 
up.     If  there  be  no  planking,  the  sides  of  the 

*  Vicat,  p.  32.— Totten's  Treussart,  p.  128. 


INGREDIENTS    OF    MORTARS.  21 

heap  are  finished  in  slopes,  which  are  finally- 
covered  by  a  layer  of  lime,  placed  there  the 
moment  after  immersion.  This,  falling  to  pow- 
der, lodges  in  the  interstices  of  the  lumps  of 
lime,  and  thus  furnishes  a  secure  protection 
against  the  air  and  moisture.* 

42.  When  a  limestone    contains  twenty  per  Hydraulic 
cent,   or  more   of   its  weight    of   clay,   it  may 
furnish  the  substance  termed  hydraulic  cement. 

Mr.  Parker,  the  discoverer  of  this  important 
building  material,  gave  it  the  improper  name 
of  Roman  cement ;  which  only  serves  to  mis- 
lead the  public,  inasmuch  as  the  Romans  never 
made  use  of  anything  of  the  kind.  The  Eng- 
lish cement,  now  known  as  Parker's  Roman 
cement,  is  obtained  by  the  slight  calcination  of 
a  limestone  containing  above  thirty  per  cent,  of 
clay,  with  some  hundredths  of  manganese  and 
carbonate  of  magnesia.  It  is  of  the  same  nature 
with  that  manufactured  in  large  quantities  in  the 
State  of  New  York,  and  probably  owes  its  supe- 
riority over  our  own  cement  (which  is  believed 
to  be  very  little),  to  the  greater  fineness  of  the 
powder  to  which  it  is  reduced. 

43.  Hydraulic  cement  stone  must  be  burned Car?  to.ba 

•    i  i  i       i    i  i         t  •      •        taken   in 

with  great  care,  though,  like  the  limestones,  it  is  burning  cc- 
properly  calcined  when  the  product  no  longer  'u 
effervesces  with  acids.f  Any  increase  of  heat, 
however,  beyond  the  point  of  complete  calcina- 
tion, greatly  impairs  its  quality;  and,  as  this 
point  is  difficult  to  determine,  cement  is  usually 
underburned,  and  gives  off  carbonic  acid  gas, 
when  treated  with  muriatic  acid.  Petot  states, 
however,  that  it  is  equally  possible  to  obtain 
hydraulic  cement  by  an  incomplete  and  a  super- 

*  Vicat,  page  33.  t  Pasley  on  Cements.  &c.  page  31. 


22  TREATISE    ON    MORTARS. 

calcination ;  but  (what  is  most  remarkable)  that, 
at  an  intermediate  point  of  calcination,  the  pro- 
duct is  almost  wholly  inert.  This  effect  is  pro- 
duced, according  to  his  view,  when  the  stone  is 
completely  calcined.  Gen.  Pasley  says,  on  the 
contrary,  and  he  is  doubtless  right,  that  it  is 
occasioned  by  carrying  the  burning  to  a  point 
beyond,  to  wit,  that  of  incipient  vitrification. 
Whichever  opinion  may  be  correct,  the  only 
proper  mode  of  burning  the  cement  stone  is  to 
expose  the  mineral  to  a  lower  degree  of  tempe- 
rature than  that  which  ordinary  limestones  re- 
quire. The  heat  requisite  for  super-calcination 
would  involve  a  larger  expenditure  of  fuel,  and 
the  cost  of  pulverizing  the  stone,  if  vitrified, 
would  be  greatly  enhanced.* 
cement  to  4.4.  As  calcined  cement  is  of  no  use  until  it 
^togted^is  pulverized,  this  is  usually  done  by  the  manu- 
facturer, to  relieve  the  purchaser  of  the  trouble 
and  expense  of  the  process.  The  powder,  thus 
prepared  for  sale,  is  secured  in  tight  casks,  lined 
with  paper,  to  preserve  it  from  the  action  of  the 
air.  Even  thus  protected,  however,  it  absorbs 
carbonic  acid  and  water  in  a  short  time,  is  rapid- 
ly deteriorated,  and  becomes  eventually  spoiled. f 
If  we  reflect,  moreover,  on  the  liability  of  the 
manufacturer  to  negligence  in  calcination  and 
pulverization,  we  see  at  once  the  absolute  neces- 
sity of  always  testing  hydraulic  cement  with 
great  care,  before  it  is  employed  in  making 
mortar. 
Mode  of  45.  When  cement  has  been  injured  by  ex- 
'Tiljur^d5  posure  to  the  air  and  moisture,  its  energy  may 
cement.  be  restored  by  burning  it  anew,  as  any  one  may 
easily  ascertain  for  himself  by  heating  a  little 

*  Toiten's  Petot,  pages  131,  182.— Pasley,  page  31. 
t  Pasley,  page  33. 


INGREDIENTS    OF    MORTARS.  23 

of  the  powder  upon  an  iron  plate  in  a  common 
fire-place.  If  it  derives  no  improvement  in  qual- 
ity from  the  second  burning,  we  may  infer  at 
once,  either  that  the  mineral  which  furnished  the 
cement  was  of  very  poor  character,  or  that  the 
calcined  product  has  been  mingled  with  inert 
foreign  matters.* 

46.  As  cement  does  not  slake  before  it  is  pul-  moj0  ?r 
verized,  even  in  water,  much  less  by  the  action  dement* 
of  the  air,  it  may  be  preserved  for  a  long  time 

in  the  condition  in  which  it  leaves  the  kiln,  if 
placed  in  a  dry  room.*  The  manufacturers  often 
keep  it  in  this  way  for  many  months,  without 
any  sensible  injury  to  its  quality.  A  fragment 
of  the  calcined  stone,  that  had  been  lying  for 
three  years  in  the  office  at  Fort  Warren,  upon 
being  reduced  to  powder  and  converted  into 
paste,  was  superior  in  energy  to  the  powders 
obtained  from  the  casks  purchased  only  a  few 
months  before.  Whenever,  then,  it  may  be 
necessary  to  transport  hydraulic  cement  to  a 
great  distance,  or  keep  it  for  any  length  of  time, 
the  constructor  might  procure  it  from  the  manu- 
facturer in  the  lumpy  state,  as  it  comes  from  the 
kiln,  and  provide  himself  with  an  apparatus  for 
grinding,  which  he  can  employ  as  the  necessities 
of  his  work  may  demand. 

47.  Cement  sets   very  rapidly,  and,   for  this  Remarks 
reason,  can  only  be  slaked  in  such  quantities  ason  cement- 
may  be  required  for  immediate  use.     Sufficient 
water  should  be  employed  to  form  a  paste  of 
medium  stiffness,  care  being  taken  not  to  drown 

the  powder,  but,  at  the  same  time,  to  wet  it 
thoroughly.  Gen.  Pasley  recommends  one-third 
of  a  measure  of  water  to  one   of  the  powder, 

*  Pasley,  pages  33,  124. 


24  TREATISE    ON    MORTARS. 

though  the  precise  quantity  must  in  general 
depend  on  the  nature  of  the  cement.  Whether 
alone  or  mixed  with  sand,  the  paste  must  always 
be  used  before  it  has  set ;  after  this  takes  place, 
it  cannot  be  disturbed  without  a  material  loss 
of  hydraulic  energy. 

SAND. 

Remarks       48.   This  substance,  which  plays  so  essential 
on  sand.   a  part  -n  tjie  compOSjtjon  of  mortars,  is  produced 

by  the  disintegration  of  the  schistose,  granitic, 
or  calcareous  rocks,  the  freestones,  &c,  through 
the  action  of  the  atmosphere  or  the  force  of 
running  waters.  The  sandy  grains,  thus  thrown 
off  from  the  decomposed  minerals,  are  trans- 
ported far  from  their  original  localities,  by  brooks 
and  rivers,  and  deposited  in  masses  along  their 
banks,  as  well  as  on  the  sea-shore.  Deposits 
of  fossil  sands  have  also  been  made,  in  places 
where  there  are  now  no  running  streams,  during 
the  partial  revolutions  of  the  earth.* 

cWsifica-  49.  Sands  may  be  classified,  with  relation' to 
'j;;1,0''  their  constituent  parts,  as  the  argillaceous,  the 
siliceous,  the  calcareous,  &c. ;  or  they  may  be 
arranged,  by  reference  to  the  size  of  the  grains, 
into  fine,  middling,  and  coarse  sands.  Con- 
structors usually  distinguish  them  into  river 
sand,  sea  sand,  and  pit  sand,  according  as  they 
come  from  these  different  localities.  The  con- 
stituent elements  of  these  three  kinds  of  sand 
are  the  same,  and  vary  only  with  the  minerals 
from  which  they  were  originally  derived.* 

choice  of  50.  The  respective  merits  of  the  several  vari- 
eties  are   still  involved  in  question.     Sand  is, 

*  Smith's  Vicat,  pages  43,  45.— Totten's  Treussart,  page  113. 


sands. 


INGREDIENTS    OF    MOIITARS.  25 

however,  an  inert  substance,  and  any  variation 
in  its  quality  must  depend  wholly  upon  the  size, 
form,  and  hardness  of  the  grains.*  Accordingly, 
pit  sand,  of  a  siliceous  or  quartzose  nature,  and 
entirely  free  from  earthy  impurities,  may  always 
be  regarded  as  the  best  ;f  its  grain  is  more  an- 
gular and  sharp  than  that  of  river  or  sea  sand, 
the  particles  of  which  are  usually  rounded  from 
constant  attrition,  and  therefore  less  adapted  for 
forming  a  compact  body  with  the  cementing 
ingredient.  It  has  not  been  universally  preferred 
by  constructors,  because  they  have  probably 
employed  it  without  freeing  it  from  the  earthy 
matters  often  mixed  with  ii.%  Very  excellent 
sands,  however,  are  frequently  obtained  on  the 
banks  of  rivers,  as  well  as  on  the  sea-shore.  Of 
the  two  kinds,  river  sands  are  to  be  preferred  to 
sea  sands,  by  reason  of  the  salts  always  existing 
in  the  latter,  and  somewhat  objectionable,  on 
account  of  their  deliquescing  properties  ;  though 
exposure  to  the  weather  soon  deprives  sea  sand, 
in  a  great  measure,  of  its  saline  matters,  and 
leaves  but  little  to  choose  between  it  and  river 
sand.<§>  With  regard  to  the  size  of  the  grains, 
experiments  show  that  there  is  an  advantage 
to  be  gained  from  the  employment  of  fine  sand 
with  the  hydraulic  limes,  though  they  establish 
nothing  with  regard  to  its  superiority  over  coarse 
sand,  in  combinations  \v\iX\  fat  lime.  || 

51.  All  the  sands  should  be  carefully  exam-  F^aminn 
ined  before  they  are   used  ;  for  river  sand  and 
even  sea  sand  are  not  always  exempt  from  earthy 
powders,  which,  experience  proves  conclusively, 
are  often  very  injurious  to  mortars.     Pure  sands, 

*  Vicat,  p.  85.  t  Rondelet,  Art  de  BAtir,  pp.  130,  132. 

t  Totten's  Treussart,  p.  113.  §  Raucourt,  p.  22. 

||  Smith's  Vicat,  p.  87. — Totten's  Treussart,  p.  105. 

3 


tion    of 

samls. 


20 


TREATISE    ON    MORTARS. 

rubbed  between  the  fingers,  should  leave  no  stain, 
and,  immersed  in  limpid  water,  should  at  once 
fall  to  the  bottom,  without  altering  the  trans- 
parency of  the  liquid  in  a  sensible  degree.* 
Should  the  water  become  muddy,  it  is  an  indi- 
cation of  the  presence  of  some  foreign  matter, 
the  nature  and  proportions  of  which  it  is  impor- 
tant to  ascertain,  as  it  may  possibly  possess  hy- 
draulic properties.  In  order  to  determine  these, 
place  a  portion  of  the  sand  in  a  vessel  of  water, 
agitate  it  thoroughly,  and  then  pour  off  the 
water  into  a  separate  vessel  of  larger  size ;  add- 
ing fresh  water  to  the  sand,  repeat  the  operation, 
until  the  granular  particles  alone  remain  in  the 
first  vessel,  after  the  decantation.  Allowing  the 
turbid  water,  resulting  from  the  several  washings 
of  the  sand,  to  remain  tranquil  for  some  hours, 
decant  it  gently,  and  the  powders  that  originally 
formed  part  of  the  substance  under  trial  will 
then  be  left  behind.  They  should  be  carefully 
dried  and  measured,  and  the  proportion,  which 
they  bear  to  the  sandy  particles,  may  now  be 
easily  determined.!  We  are  not  yet  acquainted 
with  the  properties  of  the  powders,  however  ; 
and,  with  the  view  of  discovering  if  the  sand 
is  at  all  hydraulic,  make  two  cakes  or  mixtures 
with  fat  lime,  one  with  two  measures  of  the 
powder,  the  other  with  two  measures  of  the 
sand  in  its  original  state,  to  one  of  lime  paste, 
and  test  them  in  the  mode  recommended  in 
Article  18.  If  either  cake  exhibits  hydraulic 
qualities,  the  sand  may  be  classed  as  a  puozzo- 
lana.  If  they  both  remain  soft  after  a  month's 
immersion,  we  may  infer  at  once  that  the  powder 
has  no  useful  quality.     It  should,  in  this  case, 

*  Smith's  Vicat,  p.  43.  +  Raucourt,  pp.  55,  56. 


INGREDIENTS    OF    MORTARS.  27 

be  separated  from  the  sand,  unless  it  exists  in 
small  quantity,  and  reasons  of  economy  balance 
the  injury  which  the  sand  may  experience  from 
its  presence.* 

As  to  the  sandy  particles  obtained  in  the 
analysis,  we  may  separate  them  into  coarse, 
fine,  and  middling  sands,  by  means  of  sieves, 
properly  selected,  and  ascertain,  by  measuring 
the  void  spaces  of  each,  if  they  exist  in  proper 
proportions ;  and,  if  they  do  not,  what,  kind  of 
sand  should  be  added  to  them,  to  form  the  best 
mixture  for  mortar.     See  Article  81. 

52.  When  sand  contains  earthy  impurities  to  Mode  or 
any  extent,  it  must  be  thoroughly  washed,  in  cl(3! 
order  to  be  rendered  suitable  for  mortars.  This 
may  be  done  on  the  large  scale  in  the  following 
manner,  recommended  by  Gen.  Treussart :  Near 
the  well  or  pump,  construct,  either  of  masonry, 
or,  more  economically,  of  plank,  a  basin  of  con- 
venient size,  say  eight  feet  long  and  four  feet 
wide,  with  a  depth  of  two  feet  two  inches, 
except  on  one  end,  where  the  wall  or  side  should 
be  only  fourteen  inches  in  height.  The  gap, 
thus  made  in  the  end  of  the  basin,  is  closed  by 
a  movable  plank,  which  works  in  grooves,  fitted 
to  receive  it,  in  the  side  walls.  A  layer  of  sand 
about  a  foot  thick  is  then  placed  in  the  basin, 
and  the  latter  filled  with  water  from  the  pump. 
The  sand  must  now  be  well  stirred  up  by  two 
or  three  laborers,  and,  after  it  has  been  allowed 
sufficient  time  to  fall  to  the  bottom  of  the  basin, 
the  movable  plank  is  suddenly  withdrawn,  when 
a  great  part  of  the  water  will  pass  off,  loaded 
with  the  earthy  matter.  The  operation  should 
be  repeated  until  the  water  appears  but  slightly 

*  Raucourt,  pp.  55-57. 


28  THEAT1SE    ON    MORTARS. 

turbid  ;  the  sand  is  then  taken  out  to  dry,  and 
the  process  may  be  applied  to  other  portions.* 
Use  or  53.  Sand  performs  no  chemical  part  in  mor- 
mortaia.  tars,  but  is  entirely  passive  in  its  influence  ;  it 
appears  rather  to  diminish  the  adhesiveness  or 
tenacity  of  the  limes,  and,  though  it  may  often 
add  to  their  resistance,  is  employed  chiefly  for 
reasons  of  economy.  It  is  useful,  however,  as 
an  ingredient  of  mortar,  in  some  other  respects; 
it  moderates  the  shrinkage  of  the  cementing 
matter,  making  it  uniform,  and  preventing  cracks ; 
probably  facilitates  desiccation,  and  makes  the 
induration  more  rapid. f 

Sand  diminishes  the  strength  of  hydraulic 
cement  in  every  respect,  whether  we  regard 
tenacity,  resistance,  or  the  property  of  setting 
under  water ;  though  a  mixture  of  cement  and 
sand  for  stucco  and  pointing  mortar  is  better 
than  pure  cement,  as  being  less  liable  to  crack, 
and  therefore  more  durable,  when  exposed  to  the 
sun  in  hot  weather.  In  general,  a  moderate 
portion  of  sand  is  mingled  with  cement,  for  the 
sake  of  economy,  except  in  peculiar  circum- 
stances, on  very  important  works.| 


POUZZOLANAS. 

rouzzoia-  54.  The  substance  commonly  known  as  pouz- 
'"'  zolana,  is  a  volcanic  product,  deriving  its  name 
from  the  village  of  Pouzzoles,  at  the  foot  of 
Mount  Vesuvius,  where  it  is  found  near  the  sur- 
face of  the  ground.  But  the  word  pouzzolanas 
is  here  used  as  a  general  term,  and  under  it  will 
be  comprised  all  those  products,  which,  without 

*  Totten's  Treussart,  p.  154.  t  Ibid.  p.  105. 

t  Pasley,  pp.  41,  202,  203. 


INGKEDIENTS    OF    MORTARS.  29 

containing  lime  as  a  principal  constituent,  form 
with  it  combinations,  which  possess  the  property 
of  setting  under  water. 

55.  These  substances  offer  very  important  ad-  Remarks  on 

,  .  c  .  j     pouzzoli 

vantages  in  the  improvement  ot  mortars,  ana  nas. 
deserve  particular  attention,  because  hydraulic 
cement  is  not  always  to  be  had,  and  hydraulic 
limes  often  give  mediocre  results,  unless  they 
are  mingled  with  a  certain  proportion  of  pouzzo- 
lana ;  and  the  latter  has,  moreover,  this  advan- 
tage over  the  hydraulic  limes, — its  qualities  are 
scarcely  at  all  impaired  by  exposure  to  the  air 
and  moisture. 

The  essential  constituents  of  pouzzolanas  are 
silica  and  alumina,  and  their  elements  have  in 
general  undergone,  through  igneous  action,  a 
change  in  their  primitive  mode  of  combination. 
Now,  as  the  intensity  of  this  action  may  be  very 
various,  it  is  easy  to  conceive  that  a  great  differ- 
ence may  exist  in  their  qualities,  though  their 
chemical  constitution  may  remain  the  same.* 

56.  Pouzzolanas   may    be    divided    into    two  ciassifiea- 
classes  ;  the  natural  and  artificial.     The  first  in  pouTzoiu- 
their  natural  state,  possess  the  property  of  form-      nas- 
ing    hydraulic    mixtures   with    fat    lime.      The 
second  are  obtained  by  the  calcination  of  certain 
natural  products,  which,  without  being  burned, 
would  have  no  action  upon  fat  lime  ;  but,  prop- 
erly calcined,  have  equal  efficacy  with  those  of 

the  former  class.  Under  the  head  of  natural 
pouzzolanas  may  be  comprised,  pouzzolana  prop- 
erly so  called,  tras  or  terras,  and  the  arenes. 

57.  Few  regions  exposed  to  igneous  agency  Ponzzoium 
are  without  -pouzzolana.    It  presents  itself  under    I>roper- 
various  physical  appearances.     It  is  sometimes 

*  Totten  on  Mortars,  p.  169. 

3# 


30  TREATISE    ON    MORTARS. 

pulverulent,  sometimes  in  coarse  grains  ;  and 
though  generally  of  a  brown  color,  is  also  found 
white,  black,  yellow,  gray,  red  and  violet.  A 
specimen,  analyzed  by  M.  Berthier,  gave,  in  one 
hundred  parts,  44.50  of  silica,  15.  of  alumina, 
and  8.8  of  lime,  besides  small  proportions  of 
magnesia,  oxide  of  iron,  potash,  soda  and  water.* 
Pouzzolana  has  no  cementing  properties  in  itself, 
but  its  qualities  may  be  tested  in  the  manner 
prescribed  in  Article  51.  One  measure  of  lime 
paste  to  two  of  pouzzolana  powder,  if  the  latter 
is  of  very  good  quality,  should  set  under  water 
in  four  days.  Pouzzolana  must  always  be  re- 
duced to  the  state  of  an  impalpable  powder, 
before  it  is  employed  as  an  ingredient  of  mortar, 
as  it  acts,  only  when  thus  pulverized,  with  its 
full  energy  upon  lime.  It  does  not  add  much  to 
the  tenacity  of  fat  lime,  but  augments  its  resist- 
ance in  a  remarkable  degree.  The  weaker  hy- 
draulic limes  are  always  improved  by  the  addition 
of  pouzzolana  ;  the  eminently  hydraulic  limes 
and  hydraulic  cement  are  always  injured  by  its 
use.* 
tnm.  58.  Trass  or  terras  is  obtained  near  Andernach, 
on  the  Rhine,  from  the  village  of  Brohl,  situated 
at  the  foot  of  an  extinct  volcano.  It  is  of  a 
grayish  color,  much  resembling  gray  clay  which 
has  been  calcined,  and  is  found  in  lumps  or  par- 
ticles of  various  sizes,  from  that  of  a  pea  to  that 
of  an  egg.  Its  general  properties  are  the  same 
as  those  of  pouzzolana.  Like  that  substance,  it 
is  prepared  for  use  by  being  pulverized,  and  it 
has  the  same  chemical  constituents,  though  in 
somewhat  different  proportions.  It  will  cause 
most  limes  to  harden  under  water ;  yet  Smeaton 

*  Totten's  Treussart,  pp.  52,  53.— Pasley,  pp.  182,  202,  205. 


INGREDIENTS    OF    MORTARS.  31 

regards  it.  as  inferior  to  pouzzolana,  in  some  re- 
spects. In  a  state  between  wet  and  dry,  or  of 
being  wet  and  dry  at  intervals,  it  does  not  answer 
well,  but  becomes  friable  and  crumbly.  Smeaton 
further  remarks,  that,  when  always  wet,  and  in 
a  state  most  favorable  to  its  cementing  principle, 
it  throws  out  a  substance  resembling  stalactites, 
which  becomes  in  time  very  hard,  and  deforms 
the  face  of  walls  :  indeed,  when  smoothness  and 
regularity  of  surface  are  required,  as  in  navigable 
sluices  and  the  like,  it  becomes  necessary  to  re- 
move with  instruments,  the  stony  excrescence 
which  it  forms.  This  effect  may  have  been 
produced,  however,  in  consequence  of  Smeaton's 
using  too  large  a  proportion  of  lime  with  his 
terras,  a  proportion  which  should  rarely  exceed 
the  ratio  of  one  to  one.  General  Pasley  thinks 
it  is  not  peculiar  to  trass,  and  recent  experiments 
give  the  substance  a  very  good  character.* 

59.  A  species  of  fossil  sands,  of  very  singular  Arenea. 
properties,  was  discovered  in  France,  a  few  years 
since,  by  M.  Girard  de  Caudemberg.  He  gives 
them  the  name  of  arenes,  to  distinguish  them 
from  other  sands.  They  may  be  made  into  a 
paste  with  water,  and  are  often  used  alone,  as  a 
pise,  in  building  the  walls  of  houses,  as  they 
shrink  less  than  clay,  and  resist  better  the  in- 
clemencies of  the  weather. 

But  they  possess  a  more  important  property. 
When  mingled  with  common  fat  lime,  they  form 
mortars,  which  set  under  water,  and  acquire 
great  hardness.  M.  Girard  built  several  locks 
with  mortar  composed  of  common  lime  and  the 
arenes,  and  obtained  very  good  results.  It  was 
necessary  to  use  the  pick,  to  break  up  concrete 

*  Totten's  Treussart,  pp.  52,  53,  55.— Vicat,  pp.  17S,  179. 


32  TREATISE    ON    MORTARS. 

that  had  been  made  with  them   the    year  be- 
fore.* 

Physical        60.   The  arenes  are  widely  distributed  through- 
characters       ,-n  i  .  •         r       i  ■     i     i 
of  the    out  r  ranee,  and  sometimes  round  in  beds  more 

arenes.  ^^  f^f*ty  feet  thick.  They  are  usually  discov- 
ered on  the  summit  of  hillocks,  which  form  the 
basins  of  brooks  and  rivers,  and  have  all  the 
characters  of  an  alluvial  deposit,  though  rarely 
met  with  in  valleys. 

The  color  of  the  arenes  is  very  various  :  they 
are  red,  brown,  yellow,  and   sometimes  white. 
M.   Girard  examined  several   kinds  by  repeated 
washings  and  decantation,  and  found  that  they 
were  all  composed  of  sand  mixed  with  clay,  in 
various  proportions,  from  ten  to  seventy  per  cent. 
The  sand  is  sometimes  fine,  sometimes  coarse, 
occasionally    calcareous,    but    more    frequently 
siliceous  or  mixed.* 
Energy  in-      61.  The  arenes  form,  good  hydraulic  mortars 
c^ictnation.  with  fat  lime,  when  used,  either  in  their  natural 
state,   or    after    undergoing    calcination.      Two 
mortars  containing   equal    proportions  of  crude 
energetic  arenes,  and  the  same  arenes  calcined, 
showed  no  appreciable  difference  in  their  con- 
sistence, after  a  year's  immersion  in  water.     The 
torrefaction  of  the  arenes,  however,  hastens  their 
induration  in  a  remarkable  degree.* 
rropenies       62.  Properties  resembling  those  of  the  arenes 
ar°enesein  have  also  been  recently  discovered  by  M.  Avril 
giaywacke"  in  graywacke,  and  even  granite,  when  in  a  state 
of  decomposition.     Their  hydraulic   quality  is, 
however,   feeble,   though    it    acquires    increased 
energy  by  a  slight  calcination. 
Remarks       63.  As  the  arenes  are  found  in  great  abundance 
Ua'r0<me3.e  in  Europe,  it  is  highly  probable  that  they  exist 

*  Totten's  Treussart,  p.  114. 


INGREDIENTS    OF    MORTARS.  33 

in  many  parts  of  this  country.  Engineers  should 
search  carefully  for  them,  in  the  vicinity  of  all 
the  public  works.  They  may  be  used  always 
with  economy,  and  often  furnish  the  only  means 
of  procuring  good  mortars  at  a  cheap  rate.  The 
mode  of  testing  sands  mentioned  in  Article  51, 
will  discover  their  hydraulic  properties  when  they 
exist. 

64.  When  the  natural  pouzzolanas  are  not  to  Artificial 
be  obtained,  or  only  at  considerable  cost,  they      nas. 
may  be  replaced,  at  slight  expense,  with  artificial 
products  of  equal   quality.     Clays  properly  cal- 
cined, brick  and  tile  dust,  forge  scales,  such  as 

fall  from  iron  at  a  smith's  anvil,  and  slag  from 
the  iron-foundries,  are  artificial  pouzzolanas. 

65.  Clays  are  essentially  composed  of  silica  ciays. 
and  alumina  in  variable  proportions,  but  often 
contain,  besides  these,  oxide  of  iron,  the  car- 
bonates of  lime  and  magnesia,  and  other  foreign 
matters.  They  are  earthy  substances,  variously 
colored,  and  soft  to  the  touch,  diffuse  in  water 
with  facility,  and  form  with  it  a  paste,  which, 
when  dried,  retains  its  solidity,  and  becomes  hard 

if  exposed  fo  the  action  of  fire.* 

66.  All  clays,  calcined  to  the  proper  degree,  ciaysmost 
and  reduced  to  powder,  will  afford  artificial  pouz-  selection' 
zolanas  of  better  or  worse  quality,  according  to 

their  composition.  The  clays,  most  proper  for 
selection,  are  those  which  are  greasy  to  the 
touch,  such  as  are  commonly  used  in  making 
the  various  kinds  of  earthen  ware,  and  contain 
from  a  third  to  a  half  of  alumina,  with  four  or 
five  per  cent,  of  lime. 

Lime  does  not  augment,  in  a  sensible  degree, 
the    energy  of  the   pouzzolana ;    but  clays   are 

*  Smith's  Vicat,  p.  47. 


34  TREATISE    ON    MORTARS. 

more  easily  pulverized,  and  brought  more  prompt- 
ly to  the  proper  state  of  calcination,  when  they 
contain  a  small  proportion  of  that  substance.  It 
is  therefore  important  to  ascertain  the  amount  of 
lime,  in  the  clays  under  examination,  as  we  can 
then  regulate  the  degree  of  heat  to  be  employed 
in  the  burning.* 
Mode  of  67.  The  following  method  of  examining  clays 
eXclays'.ns  is  recommended  by  General  Treussart.  Take 
a  little  of  the  crude  earth,  and  pour  upon  it 
dilute  muriatic  or  nitric  acid,  or  even  strong 
vinegar.  Should  there  be  no  effervescence,  the 
clay  is  without  any  carbonate  of  lime,  and,  in 
such  a  case,  should,  in  general,  be  highly  cal- 
cined. If  effervescence  takes  place,  we  may 
infer  the  presence  of  some  carbonate,  the  propor- 
tion of  which  is  determined  as  follows.  A  por- 
tion of  the  clay,  having  been  dried  at  a  gentle 
heat,  is  accurately  weighed,  and  then  diffused  in 
a  small  quantity  of  water.  Muriatic  acid  is  now 
poured  on  gradually,  as  long  as  there  is  any  effer- 
vescence, and  the  liquid  is  then  filtered  or  care- 
fully decanted.  The  clay  remaining  behind 
should  be  washed  in  a  large  quantity  of  water, 
which  is  once  more  decanted,  and  the  residue 
having  been  dried  at  the  same  gentle  heat  as 
before,  must  be  finally  weighed  again. 

If  the  loss  of  weight  is  one  tenth,  the  clay 
probably  contains  about  that  proportion  of  car- 
bonate of  lime,  which  has  been  dissolved  out  by 
the  acid.  In  this  case,  the  burning  of  the  clay 
should  be  conducted  at  the  same  temperature,  as 
that  required  to  produce  "pale  bricks."  Should 
the  clay  lose  only  four  or  five  per  cent,  of  its 
weight,  it  ought  to  be  burned  about   as  much 

*  Totten's  Treussarl.  pp.  129,  130. 


INGREDIENTS    OF    MORTARS.  35 

"as  well  burned  bricks."  When  it  loses  more 
than  a  tenth,  the  heat  proper  for  burning  tiles 
should  be  employed,  and,  in  general,  the  clay 
must  be  burned  less,  as  its  loss  of  weight  by  the 
acid  is  greater. 

Some  of  the  loss  of  weight,  in  the  above  ex- 
periment, may  have  been  due  to  the  presence  of 
carbonate  of  magnesia  in  the  clay  under  trial. 
The  amount  of  this  substance  may  be  ascertained 
by  adding  lime-water  to  the  liquid  after  the  de- 
cantation  ;  the  magnesia,  if  contained  in  the  solu- 
tion, would  then  be  precipitated,  and  after  being 
well  dried,  might  be  weighed.  The  quantity  of 
lime  could  in  this  way  be  more  correctly  ascer- 
tained ;  but  as  Gen.  Treussart  does  not  speak  of 
any  deduction  on  account  of  magnesia,  it  is 
probable  that  this  substance  may  affect  the  cal- 
cination similarly  with  lime.* 

68.  Having  selected  a  clay,  it  is  well  to  test  it  Mo.ic  of 
further,  by  reducing  it  to  powder,  and  strewing  ^drauii/" 
a  layer,  half  an  inch  thick,  upon  an  iron  plate,  iualltle8- 
heated  to  a  point  between  cherry  red  and  forging 
heat.  The  powder  should  be  stirred  continually 
with  a  rod,  in  order  that  the  particles  may  be  uni- 
formly calcined  ;  and  left  on  the  iron  plate  for  a 
space  of  time,  varying  according  to  the  compo- 
sition of  the  clay,  from  five  to  twenty-five  min- 
utes. When  the  clay  is  sufficiently  calcined,  its 
hydraulic  qualities  may  be  ascertained,  by  ming- 
ling a  little  of  the  powder  with  the  paste  of  fat 
lime,  which  has  been  slaked  for  some  time,  in  the 
proportion  of  one  of  the  paste  to  two  of  the  clay. 
The  mortar  thus  formed,  should  be  immersed,  as 
advised  in  Article  18.  In  examining  it  from  day 
to  day,  it  would  be  well  to  remove  the  turbid 

*  Totten's  Treussart,  p.  93. 


36 


TREATISE    ON    MORTARS. 


water  from  the  surface,  which  is  generally  cov- 
ered with  a  semi-fluid  matter,  and  may  be  lightly 
cleaned  with  a  rag.  If  the  cement  is  energetic, 
the  mortar  should  harden  in  three  or  four  days. 
If  the  mixture  has  only  a  weak  consistence  after 
the  lapse  of  a  month,  the  pouzzolana  should  be 
regarded  as  unfit  to  be  employed.* 

Remarks.  69.  By  the  simple  means  above  indicated,  the 
constructor  may  acquaint  himself  with  the  prop- 
erties of  the  various  clays  in  his  vicinity,  as  well 
as  the  degree  of  calcination,  which  each  variety 
may  require.  He  is  then  prepared  to  manufac- 
ture pouzzolanas  on  the  large  scale  in  furnaces 
(to  be  described  hereafter),  which  should  always 
be  so  arranged  as  to  supply  the  clays  with  a  cur- 
rent of  air  during  the  calcination ;  experience 
having  shown,  that  clays  thus  burned,  are  much 
more  energetic  than  when  the  air  is  excluded. 

Brick  aid  70.  Brick  or  tile  dust,  with  the  properties  of 
good  pouzzolana,  may  be  obtained  by  pulverizing 
bricks  or  tiles,  selected  from  any  brick-yard.  We 
may  take  bricks  of  various  colors,  reduce  them 
to  an  impalpable  powder,  and  test  the  powder  in 
the  manner  prescribed  in  the  preceding  Articles; 
or  we  can  determine  whether  "  pale,"  M  well 
burned  "  or  "  too  much  burned  "  bricks  should 
be  selected,  by  ascertaining  the  proportion  of 
lime  contained  in  the  bricks.    (Art.  67.) 

Bricks  and  tiles  afford  pouzzolanas  of  excellent 
quality,  though  not  so  good  as  those  obtained  by 
calcining  well  selected  clays,  as  a  coarser  mate- 
rial is  commonly  used  by  brick-makers.f 
Forge-         71.  Forge-scales,  as  well  as  the  siftings  of  iron 

Ecales  and  . 

minion,    stone,  after  calcination  in  the  iron-furnaces,  called 
minion,  were  used  as  pouzzolanas  by  Smeaton, 

*  Smith's  Vicat,  p.  50. — Totten's  Treussart,  p.  93. 
t  Pasley,  p.  ISO. 


INGREDIENTS    OF    MORTARS. 

and  with  excellent  effect.  Both  should  be  sifted 
clean  from  dust  and  glassy  slag,  and  reduced  to 
fine  powder,  by  grinding  in  a  mill.  Smeaton 
regarded  forge-scales,  when  thus  prepared,  to  be 
equivalent  to  an  equal  quantity  of  natural  trass 
or  pouzzolana.  Minion,  the  rust  of  iron,  or  iron 
ore  burnt,  powdered  and  sifted,  might  be  substi- 
tuted in  place  of  half  a  similar  quantity  of  those 
substances,  with  an  equally  good  result.* 

72.  The  vitrified  substance,  called  slag  at  the 
iron  foundries,  is  often  used  alone  as  a  cement, 
without  any  admixture  with  lime.  It  is  ground 
to  very  fine  powder  on  a  cast-iron  bed,  and  then 
made  into  a  paste  with  water.  This  cement, 
Capt.  Smith  states,  was  employed  in  laying  the 
ashlar  work  of  the  docks  at  Sunderland,  in  1835  ; 
though  for  other  parts  of  the  same  structure,  a 
mixture  of  two  parts  of  lime  paste  with  one  of 
the  powdered  slag  was  preferred,  probably  for 
reasons  of  economy.  The  masonry  laid  with  it, 
is  kept  dry  for  a  couple  of  days,  during  which 
time  it  sets.  It  continues  afterwards,  however, 
to  indurate  sloivly,  and  acquires  at  length  a  stony 
hardness.* 

*  Smith's  Vicat,  p.  50. 


38  TREATISE    ON    MORTARS. 

CHAPTER    III. 

ON  THE  GENERAL  COMPOSITION  OF  MORTARS. 

Mortare  73.  The  object  which  we  propose  to  attain, 
in  mingling  sands  with  a  cementing  material,  is 
to  form,  as  cheaply  as  possible,  compositions, 
which,  exposed  to  all  vicissitudes  of  weather, 
and  even  placed  under  water,  may  nevertheless 
become  hard  and  solid,  attach  themselves  strongly 
to  building  materials,  and  attain,  in  the  end,  a 
resistance  superior  to  all  disturbing  forces.  Such 
combinations  are  called  mortars.* 

General  74.  Mortars  are  sometimes  made  of  the  cement- 
ing materia],  without  the  addition  of  any  gran- 
ular matter,  but  are  more  usually  composed  of 
solid  particles,  insoluble  in  water,  and  of  bodies 
partially  fluid,  which  serve  to  unite  the  former, 
by  enveloping  them.  Combinations  of  similar 
character  are  often  found  in  the  mineral  king- 
dom. Egyptian  jasper  is  merely  an  assemblage 
of  particles  of  quartz,  united  by  a  siliceous  ce- 
ment ;  granite,  an  union  of  quartz  and  mica,  the 
intervals  of  which  are  filled  with  feldspar ;  and 
the  pudding  stones  of  every  species  are  true 
natural  mortars.  Of  these  mineral  compositions, 
the  hardest  are  those  which  contain  quartz,  and 
their  hardness  increases  with  their  proportion  of 
this  substance.  Their  resistance,  however,  to  a 
force  of  traction,  or  compression,  is  not  alone 
dependent  upon  quartz  ;  many  granites  are  less 
strong,    in   this   respect,    than   some   calcareous 

*  Raucourt,  p.  8. 


remarks 
upon  mor- 
tars. 


COMPOSITION    OF    MORTARS.  39 

stones  much  less  hard,  and  when  the  feldspar 
undergoes  decomposition,  granites  become  friable, 
almost  without  coherence,  and  entirely  incapable 
of  resisting  pressure.  Neither  is  it  enough,  that 
the  cement  uniting  the  harder  particles  of  the 
mineral,  should  have  great  cohesion  ;  that  which 
binds  together  the  marbles  and  padding  stones, 
may  be  equally  strong  with  feldspar,  while  the 
duration  and  resistance  of  those  minerals  cannot 
be  compared  with  granitic  stones.  We  may 
observe,  then,  that  the  resistance  of  mortars  in 
general,  is  composed  of  three  parts,  essentially 
distinct,  viz.  : 

1st.  The  constant  resistance  of  the  enveloped 
parts,  generally  designated  by  the  name  of  sands. 

2d.  The  resistance,  varying  with  time,  of  the 
enveloping  parts,  or  cementing  ingredient. 

3d.  The  force  of  adhesion  of  the  constituent 
parts,  which  may  be  of  two  kinds  ;  one  resulting 
from  the  affinities  existing  between  them,  the 
other  arising  from  the  penetration  of  the  cement- 
ing material  into  the  interstices  of  the  sands.* 

75.  From  the  foregoing  remarks,  it  will  readily    General 
appear,  that  any  inert  substance,  which  is  added  prcomposi-" 
to  a  cement,  with  the  view  of  making  mortar,  tlontarsm0l~ 
should  be  in  particles  or  grains  ;  no  soft,  earthy, 
or  pulverulent  substance  being  fit  for  the  purpose. 
It  is  equally  apparent,  on   the  other  hand,  that 
the   cementing  matter  should  be   in   the   finest 
state  of  division  to  which  it  can  possibly  be  re- 
duced. 

We  may  infer  farther,  that  the  cement  can  be 
improved  by  the  addition  of  sand,  only  when  the 
grains  of  the  latter  are  at  least  as  hard  as  the 
greatest  degree   of  hardness  which  the  cement 

*  Raucourt,  pp.  8,  24,  25. 


40 


TREATISE    ON    MORTARS. 

can  attain,  and  the  attraction  between  the  mole- 
cules of  the  cement  and  the  particles  of  the  sand 
exceeds  the  attraction  of  the  molecules  of  cement 
for  each  other.* 

Were  this  the  case  with  the  sands  and  cements 
commonly  employed  in  making  mortar,  it  is 
obvious  that  a  combination  of  these  two  sub- 
stances would  possess  its  maximum  of  resistance, 
1st,  when  the  grains  of  sand  were  so  various  in 
size  as  to  afford  the  greatest  possible  mass  in  a 
given  volume  ;  and  2dly,  when  the  cementing 
material  exactly  filled  up  their  interstices,  or  void 
spaces.  Any  addition  of  the  cement,  beyond  this, 
would  only  do  injury,  for  the  same  reason,  that 
a  superabundance  of  feldspar  always  weakens 
granite.  Experiments,  however,  do  not  show, 
that  the  cohesion  of  all  the  mortar  cements  is 
inferior  to  their  power  of  adherence  to  the  par- 
ticles of  sand.  Vicat  thinks,  and  Pasley  and 
Petot  agree  with  him,  that  such  is  the  case  with 
the  hydraulic  limes,  while  the  contrary  seems  to 
obtain  with  rich  lime  and  hydraulic  cement.f 
Whether  this  be  true  or  not,  however,  resistance 
or  solidity  is  not  the  only  quality  which  is  desir- 
able in  mortars;  it  is  equally  important,  that  they 
should  possess  tenacity  or  adhesiveness,  and  it 
by  no  means  follows,  that  a  mortar,  composed 
like  the  one  above  mentioned,  would  be  the  most 
tenacious  ;  we  may  infer,  on  the  contrary,  that 
the  capacity  of  the  cementing  ingredient  for 
binding  materials  together  would  be  greatly  im- 
paired by  such  a  proportion  of  sand.  Experi- 
ments not  only  prove  this,  but  they  also  go  to 
show  that  the  resistance  of  mortars  made  with 
rich  lime,  or  a  mixture  of  rich  lime  and  hydraulic 

*  Encyclopedia  Britannica,  Art.  Masonry. 

t  Smith's  Vicat.  p.  85.— Pasley,  p.  203.— Raucourt,  p.  27. 


COMPOSITION    OF    MORTARS.  41 

cement,  is  always  diminished  by  the  addition  of 
sand.  They  establish,  that  rich  lime  attaches 
neither  quartz  nor  any  stony  substance,  and  that 
the  admixture  of  any  such  inert  matter  with 
hydraulic  cement,  in  every  way  impairs  its 
strength.  The  sands,  therefore,  perform  no 
chemical  part  in  the  composition  of  such  mor- 
tars, though  they  have  the  effect  of  causing  the 
rich  limes  to  harden  more  quickly,  and  make 
them,  as  well  as  hydraulic  cement,  less  liable  to 
crack  in  drying,  which  is  often  a  great  advan- 
tage.* 

Sand  is,  however,  the  least  costly  ingredient 
of  mortar,  and  economy  recommends  its  use  in 
as  large  quantities  as  possible.  Under  this  view, 
it  becomes  important  to  know  the  minimum 
amount  of  cementing  matter,  which  every  mor- 
tar must  contain  ;  and  we  may  readily  infer,  that 
the  cheapest  admissible  combination  must  be  that 
in  which  the  void  spaces  of  the  sand  are  entirely 
filled  by  the  cement  employed. 

76.  Starting  then  with  the  principle,  that  the  _Mo<ic  of 
minimum  amount  of  cementing  matter  is  deter- 
mined by  the  measure  of  the  interstices  of  the 
sand,  it  becomes  necessary  to  explain  some  con- 
venient mode  of  arriving  at  this  measure.  This 
is  done  by  filling  a  vessel,  of  known  capacity, 
with  the  sand,  compacted  as  much  as  possible, 
and  then  adding  water  until  all  the  interstices 
are  filled.  The  proportion  of  water  thus  used, 
to  the  whole  volume  of  sand,  furnishes  the 
measure  of  the  void  spaces.  The  sand  under 
trial  must  be  dry  and  siliceous  ;  otherwise,  the 
water  which  it  may  contain  or  absorb,  should  be 
taken  into  account.f 

*  Totten  on  Mortars,  pp.  105,  201,  235,  253. 
t  Raucourt,  p.  29. 

4  # 


measuring 

voids 


42  TREATISE    ON    MORTARS. 

specific        77.  Another  mode  of  measuring  the  interstices 
'ployed ein  of  sands  is  recommended  by  Capt.  Smith,  of  the 
°bvoi'dl?g  Madras  Engineers.     The  specific  gravity  of  si- 
liceous or  quartzose  sands  was  found  by  a  mean 
of  various  experiments  to  be   2.6,  the  same  as 
that   of   cmartz.     A  cubic   foot  of   it,   if   solid, 
would    therefore    weigh    162|    pounds,   since   a 
cubic  foot  of  water  weighs   1000  ounces.      We 
have  only,  then,  to  ascertain  the  difference  be- 
tween  1624-  pounds  and  the  weight  of  a  cubic 
foot  of  the  sand,  condensed  as  much  as  possible, 
in  order  to  obtain  the  measure  of  its  interstices, 
or    the    least    proportion    of    cementing    matter 
necessary  to  bind  its  particles  together.* 
Results        78.   Experimenting  with  various  sands,  by  the 
o^sands'.'  first  of  the   above   methods,  Col.  Raucourt  ob- 
tained the  following  mean  results : — 

For  coarse  sands,  the  grains  of  which  were 
from  one  to  two  lines  (one  to  two  twelfths  of 
an  inch)  in  diameter,  he  found  the  void  spaces 
to  amount  to  five  twelfths  of  the  volume. 

For  middling  sands,  with  grains  of  half  a 
line,  two  fifths  of  the  volume. 

For  fine  sands,  with  grains  of  one  tenth  of  a 

line,  one  third. f 

Mode  of       79.  When   we   have   sands  of  various    sizes, 

pmpmtionlthey  may  be  mixed  together  with  great  economy 

ofsands6d  °f    cementing   matter ;    the   fine   sands,   in   this 

case,  fill  up  the  interstices  of  the  coarser  kinds, 

and    greater    density   is  obtained   in    the    same 

volume.     When   the  diameters  of  the  grains  of 

one  kind  are  tenfold  those  of  another,  the  proper 

proportions  to   be  mixed  with  each  other  may 

be  ascertained  mechanically.     This  is  done,  by 

placing  a  given  measure  of  the  coarsest  sand  in 

*  Smith's  Vicat,  p.  45.  t  Raucourt,  p.  29. 


COMPOSITION    OF    MORTARS.  43 

any  vessel,  of  convenient  size  to  be  shaken 
easily.  A  portion  of  the  sand,  with  grains  of 
middling  size,  should  now  be  measured,  and 
poured  gradually  upon  the  first,  the  vessel  being 
well  jarred,  to  cause  the  two  to  mix  thoroughly. 
As  soon  as  the  coarse  sand  appears  to  increase 
in  volume,  the  experimenter  should  cease  adding 
to  it,  as  its  voids  are  then  occupied  by  the  mid- 
dling sands  as  far  as  possible.  The  quantity 
of  the  latter  remaining  will  indicate  the  quantity 
that  has  been  added  to  the  coarse  sand.  We 
may  proceed  in  a  similar  way  to  use  sands  of 
various  degrees  of  fineness,  and  can  thus  learn 
the  proportions  of  each  kind,  which,  mingled 
together,  will  yet  give,  very  nearly,  the  same 
volume  as  the  coarse  sand  alone. 

When  the  sands  do  not  vary  much  in  the  size 
of  the  grains,  we  may  find  out,  approximately, 
by  calculation,  the  quantities  of  each  kind  that 
should  be  mixed  together,  after  having  previous- 
ly ascertained  the  measure  of  their  respective 
voids. 

A  mixture  of  the  sands  having  been  made, 
the  voids  of  the  resulting  mass  may  be  measured 
by  either  of  the  modes  mentioned  before,  or  they 
may  be  arrived  at  by  subtracting,  from  the  known 
interstices  of  the  coarse  sand,  the  volume  of  the 
added  sands,  diminished  by  their  respective  in- 
terstices.* 

80.   By  means  of  the  processes  above  detailed,    Mode  of 
we  can  always  learn  the  minimum  amount  of i^redienuL 
cementing  matter,  which  the  sands  made  use  of 
may  require ;  and  have  only  to  mingle  the  two 
substances  in  the  proportions  thus  determined, 
in  order  to  obtain  the  cheapest  mortars.     The 

*  Raucourt,  pp.  30,  31. 


44  TREATISE    ON    MORTARS. 

most  correct  results,  in  practice,  would  always 
be  obtained  by  weighing  the  ingredients ;  but, 
as  this  is  attended  with  some  expense,  recourse 
is  usually  had  to  measuring  them. 

Four  modes  of  measuring  lime  have  been 
employed,  and  all  of  them  are  attended  with 
some  uncertainty.  The  most  ordinary  mode  is 
to  measure  it  in  lumps,  as  it  comes  from  the 
kiln  ;  a  second  method  is  to  measure  it  in  slaked 
lime  powder;  a  third,  in  quick  lime  powder; 
and  a  fourth,  in  slaked  lime  putty  or  paste. 

The  first  method  is  usually  employed  by 
builders,  when  their  works  are  not  on  a  large 
scale,  and  is  always  supposed  to  be  adopted,  if 
nothing  be  said  to  the  contrary.  It  is  obviously 
very  imperfect,  as  almost  every  lime  yields  a 
different  volume  of  paste.  The  method  of 
measuring  in  slaked  lime  powder,  though  recom- 
mended by  Smeaton,  has  not  been  employed  to 
any  great  extent,  by  reason,  probably,  of  its  in- 
convenience. The  third  method,  in  which  the 
quick  lime  is  supposed  to  be  reduced  to  powder, 
involves  the  necessity  of  grinding  and  sifting, 
and  is  attended,  therefore,  with  so  much  expense, 
as  to  forbid  its  use  almost  entirely,  even  were 
there  no  other  objections  to  its  employment. 
The  fourth  method  has  been  adopted  at  the 
public  works  in  Boston  Harbor,  and  may  be 
regarded  as  the  most  convenient  and  economical, 
in  all  large  operations.  With  a  little  care,  as 
great,  if  not  greater,  uniformity  can  be  obtained 
by  measuring  in  this  way,  as  by  either  of  the 
other  modes ;  and  I  will  therefore  suppose  it  to 
be  employed,  in  all  the  subsequent  pages.  It 
may  be  sometimes  more  convenient,  in  making 
mortar  in  a  small  way,  to  measure  the  quick 
lime  in  the  lumpy  state,  or,  if  hydraulic  cement 


COMPOSITION    OF    MORTARS.  45 

be  used,  to  measure  it  in  the  state  of  powder; 
but  it  is  always  easy  to  ascertain,  by  experiment, 
the  change  of  bulk  which  either  material  under- 
goes in  slaking,  and  then  substitute,  in  place  of 
the  paste,  its  equivalent  of  unslaked  cementing 
matter.* 

The  density  of  sand  also  varies  very  much 
with  its  condition  of  wetness  or  dryness,  and 
with  the  manner  in  which  it  is  thrown  into  the 
measure.  Experiments,  therefore,  should  always 
be  resorted  to,  before  fixing  the  proportions  of 
ingredients,  in  order  to  discover  the  due  allow- 
ance to  be  made  in  the  quantity  of  sand,  in  con- 
sequence of  this  variation. 

In  the  following  proportions,  the  sand  is  sup- 
posed to  be  at  its  maximum  density,  and  the 
cementing  ingredient  to  be  measured  in  paste, 
of  somewhat  firmer  consistence  than  mortar, 
which  is  properly  tempered  for  masons'  use. 

81.  Recurring  now  to  Article  78,  we  see  that  Minimum 
the  cheapest  admissible  mortars  are  those  in  ofOPcementS- 
which  we  add,  in=  .infe" 

'  client. 

To  twelve  measures  of  coarse  sand,  five  of 
the  cementing  ingredient. 

To- five  measures  of  the  middling  sands,  two 
of  the  cement. 

To  three  measures  of  fine  sand,  one  measure 
of  the  cement. 

And,  if  economy  be  the  chief  object,  the 
above  rule  should  be  followed,  as  one  or  the 
other  of  the  above  sands  is  at  our  disposal.  If 
all  the  various  kinds  of  sand  can  readily  be 
obtained,  we  may  mingle  them  together  in 
proper  proportions,  and  diminish  still  more  the 
amount  of  cementing  material  otherwise  neces- 
sary. 

*  Pasley,  p.  209. 


46 


TREATISE    OX    MORTARS. 


Economy       82.  A  single  example  will  show  the  economy 

in  mixing       c  •  •         i  it  ,i 

sands,  oi  using  mixed  sands.  Let  us  suppose  that  we 
have  sixty  measures  of  coarse  sand,  to  be  used 
in  making  mortar.  If  no  other  sand  was  mixed 
with  it.  we  see,  from  Article  81.  that  the  mini- 
mum amount  of  cement  required  would  be 
twenty-five  measures.  But,  examining  the  pro- 
portions of  void  spaces  in  the  different  kinds 
of  sand,  we  find  that  fifteen  measures,  at  least, 
of  fine  sand,  may  be  added  to  the  sixty  meas- 
ures of  coarse  sand,  without,  in  any  degree,  alter- 
ing its  volume.  The  twenty-five  parts  of  void 
spaces  in  the  coarse  sand  would  then  be  reduced 
to  ten  ;  but  the  void  spaces  in  the  fifteen  meas- 
ures of  added  sand  occupy  three  parts;  these 
being  added  to  the  preceding  ten,  the  sum  of  the 
voids  to  be  filled  with  the  cement  will  then  be 
only  thirteen,  and  the  great  saving  of  nearly 
one-half  of  the  costly  cementing  ingredient  is 
thus  effected  by  the  mixture  of  but  two  sands. 
Reasons  for  83.  Mortars  formed  upon  the  principle  above 
proportions5 mentioned  (as  previously  remarked),  are  the 
of  cement.  very  cheapest  that  are  admissible.  Such  mor- 
tars, however,  would  not  give  good  results  in 
practice,  and  a  larger  proportion  of  the  cement 
than  that  indicated  in  Article  81  ought  to  be 
mingled  with  the  sand,  on  several  accounts. 

The  first  reason  has  reference  to  the  shrink- 
age, which  fat  limes  undergo  in  drying  ;  on  this 
account,  the  proportions  of  cementing  matter 
above  prescribed  must  always  be  augmented, 
when  such  limes  are  employed.  This  necessity, 
however,  becomes  less  urgent,  as  the  lime  is 
more  hydraulic  in  its  character,  and  scarcely  at 
all  obtains  in  the  case  of  hydraulic  cement. 

The  second  reason  is  derived  from  the  imper- 
fection of  the  manipulation.     It  sometimes  hap- 


COMPOSITION    OF    MORTARS.  47 

pens,  that  the  proportion  of  cementing  matter, 
indicated  in  Article  SI,  causes  an  increase  of 
volume  in  the  sand.  This  shows  that  the  voids 
of  the  latter  are  not  entirely  filled  ;  and  it  is 
always  well,  in  such  a  case,  to  add  to  the  ce- 
ment, before  used,  a  quantity  equal  to  the  aug- 
mentation of  the  mixture.* 

In  the  third  place,  as  before  observed,  a  mortar 
composed  on  the  principle  in  question,  would  not 
possess  the  requisite  tenacity  for  binding  mate- 
rials-together. 

For  these  various  reasons,  it  would  generally 
be  advisable  to  increase  the  proportions  of  ce- 
menting matter,  mentioned  in  Article  81,  about 
one-half. 

84.  Those  proportions  suppose  the  cements  Af"°Ynaenrct9 
employed  to  contain  no  sandy,  inert  matters,  matters  in 
As  this,  however,  is  far  from  being  always  the 

case,  they  should  be  carefully  examined  in  the 
manner  recommended  in  Chapter  I.,  in  order  to 
discover  if  they  are  free  from  all  such  sub- 
stances. 

When  sand  is  present,  it  should  be  regarded 
as  so  much  sand  already  added,  and  a  deduction 
of  the  amount,  whatever  it  may  be,  must  always 
be  made  from  the  proportion  which  might  other- 
wise be  mingled  with  the  cement. 

85.  Pouzzolana  is  nothing  more  than  a  mix-Ru,e,intha 

3  ujeofpouz- 

ture  of  sand  and  baked  earth,  possessing  hydrau-  zoiana. 
lie  properties;  and,  when  the  cementing  matter 
is  a  combination  of  this  substance  with  lime, 
the  same  rule  as  in  other  cases  should  be  fol- 
lowed, in  regulating  the  proportions  of  ingre- 
dients in  mortars.  The  sand  which  the  pouzzo- 
lana may  contain  should  always  be  measured  by 

*  Raucotr.t.  p.  32. 


48 


TREATISE    ON    MORTARS. 


Practical 
rule  in 
making 

mortars. 


Remarks. 


careful  experiment  (Article  51),  and  deducted 
from  the  amount  which  might  be  added  to  the 
cement,  if  no  impurities  existed  in  the  pouzzo- 
lana. 

Smeaton's  rule  with  this  substance  was,  to 
diminish  the  quantity  of  sand  which  would 
otherwise  be  used,  by  the  quantity  of  pouzzo- 
lana  employed.  So  that,  if  a  lime  made  good 
mortar  with  two  measures  of  sand,  without  any 
other  admixture,  and  one  measure  of  pouzzolana 
was  added  to  it  in  order  to  increase  its  energy, — 
in  that  case,  only  one  measure  of  sand  should 
enter  into  the  composition.* 

In  making  mixtures  of  fat  lime  and  pouzzo- 
lana, it  is  better,  in  general,  to  err  from  a  defi- 
ciency, rather  than  an  excess  of  lime  ;  while  the 
contrary  rule  should  obtain  with  the  eminently 
hydraulic  limes. f 

86.  Though  any  addition  of  sand  impairs  the 
strength  of  hydraulic  cement,  a  moderate  quan- 
tity is  usually  mixed  with  it,  for  the  sake  of 
economy ;  and  experience  shows  that  very  good 
mortar  may  be  made,  by  mingling  the  two  to- 
gether, in  the  proportions  of  one  volume  of 
hydraulic  cement  paste  to  one  and  a  half  vol- 
umes of  sand,  the  grains  of  the  latter  being  of 
medium  size. 

When  this  substance  is  mingled  with  fat  lime, 
with  the  view  of  making  hydraulic  mortar,  a 
convenient  rule,  which  works  well  in  practice, 
is  to  add  two  volumes  of  sand  for  each  volume 
of  lime  paste,  and  one  and  a  half  volumes  of 
sand  for  each  volume  of  hydraulic  cement  paste. 

87.  It  may,  in  general,  be  observed,  with 
regard   to    the    various   ingredients  of   mortars, 


Pasley,  p.  1S4. 


t  Vicat,  p.  68. 


COMPOSITION    OF    MORTARS.  49 

that  the  proportions  in  which  they  are  mingled 
together  must  depend  upon  the  object  to  be 
attained,  as  well  as  the  nature  of  the  materials, 
which,  in  every  case,  will  modify  any  rule  that 
might  be  given.  The  constructor,  having  deter- 
mined his  proportions,  however,  in  accordance 
(as  far  as  possible)  with  the  considerations  con- 
tained in  the  preceding  articles,  should  proceed, 
in  the  next  place,  to  bestow  some  personal  atten- 
tion on  the  manipulation  of  the  ingredients. 
This  is,  too  often,  left  entirely  to  the  manage- 
ment of  indiscreet  workmen,  through  whose 
negligence  the  best  materials,  combined  in  the 
best  proportions,  may  be  completely  spoiled. 

88.  Mortars  ought  always,  if  possible,  to  be  Mortar*  to 
prepared  under  cover,  not  only  to  avoid  the  rapid     under 
desiccation  which  takes  place   in   summer,  but 

the  equally  serious  inconvenience  of  having 
them  drowned  in  the  rainy  season.  In  either 
case,  their  qualities  would  be  impaired ;  but  a 
hydraulic  mortar,  if  permitted  to  dry  too  rapidly, 
may  lose  the  whole  of  its  energy.*  Moreover, 
as  the  pouzzolanas.  as  well  as  hydraulic  cement, 
should  always  be  used  in  the  state  of  impalpable 
powders,  some  loss  of  material  might  be  incurred, 
in  large  operations,  during  the  prevalence  of  high 
winds,  unless  the  mortar-mill  was  sheltered  from 
their  action. 

89.  The  ingredients  of  all  mortars  should  be    M?<1.cof 

.  mixing 

thoroughly  mixed  together,  so  as  to  form  a  per-  mortars. 
fectly  homogeneous  mass.  With  this  view, 
sufficient  water  may  be  added  to  bring  the 
whole  to  the  condition  of  a  soft  paste,  care 
being  taken,  at  the  same  time,  not  to  drown  the 
compound.  In  this  state,  the  ingredients  are 
incorporated  with  each  other  more  perfectly  and 

*  Smith's  Vicat,  p.  93. 

5 


50  TREATISE    ON    MORTARS. 

more  economically ;  and  the  mortar,  too,  may 
be  somewhat  thin  with  advantage,  as,  otherwise, 
it  is  apt  to  become  so  dry,  before  it  is  used,  as 
to  lose  some  of  its  good  qualities,  and  to  require 
tempering  with  a  further  addition  of  water, 
which  is  always  to  be  avoided,  if  possible.  The 
common  idea,  that  every  good  mortar  must  needs 
"  be  worked  with  the  sweat  of  the  laborer,"  has 
induced  much  unnecessary  expense,  and  is  be- 
lieved to  be  entirely  erroneous.* 

In  making  mortars  with  mixed  sands,  it  is 
well  to  commence  by  adding  only  the  finest 
sand  to  the  cementing  ingredient.  When  these 
two  are  thoroughly  incorporated,  we  may  mingle 
with  the  compound  a  coarser  sand ;  and  this 
latter  being  well  mixed  with  it,  the  sand  next  in 
order  of  coarseness  may  be  added,  the  operation 
being  thus  continued,  until  the  coarsest  material 
has  been  employed.  In  the  first  case,  the  ce- 
ment envelopes  the  fine  sand,  the  combination 
of  the  two  then  envelopes  the  coarser  sand,  and 
so  on.  This  mode  of  mixing  the  ingredients 
produces  the  most  homogeneous  result,  and  the 
best  mortar.f  For  a  similar  reason,  mortar  made 
with  a  machine  is  superior  to  that  made  by  hand  ; 
and  it  should  be  prepared  by  such  means,  in  all 
operations  on  a  large  scale.  A  very  convenient 
mill,  employed  for  this  purpose  at  Fort  Warren, 
will  be  described  hereafter,  when  this  subject  is 
resumed  in  treating  of  the  preparation  of  mortars. 

90.  I  will  close  this  chapter  with  an  extract 
from  Smeaton's  Essay  on  Water  Cements,  ex- 
hibiting the  proportions  of  twenty  different  com- 
positions, employed  by  him  in  the  construction 
of  the  Eddystone  Lighthouse,  and  other  works.J 

*  Totten's  Treussart,  p.  9.     t  Raucourt,  p.  80.    t  Vicat,  p.  193. 


COMPOSITION    OF    MORTARS. 


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O  O  ^  l-> 
«0  O  M  W 


W-KH  HMHW        cr  S 


w  co  co  to  i-i : 


■u.  iu  ic>.  co  to  to 


OHH  MtOCO! 


o-a> 


The  materials  in  the  above  mixture  were  measured  dry.    The  lime  in  powder 
was  thrown  into  the  bushel  and  "  stricken,"  but  not  beaten  nor  pressed  down. 


TREATISE    ON    MORTARS. 


CHAPTER    IV. 

ON  THE  RESISTANCE  OF  MORTARS. 

Remarks.  91.  We  have  supposed,  in  a  preceding  chapter, 
that  a  cement  or  mortar  has  set,  when  it  bears, 
without  depression,  a  wire  one  twenty-fourth  of 
an  inch  in  diameter,  and  loaded  to  weigh  one 
pound.  Now,  after  this  condition  has  obtained, 
the  mortar  still  goes  on  constantly  to  harden, 
and,  according  to  its  quality,  acquires  in  a  defi- 
nite time,  a  certain  amount  of  strength.  It  there- 
fore becomes  important  to  know  some  simple 
means  of  measuring  the  resistance  of  mortars,  at 
different  intervals  of  time  after  their  preparation  ; 
and  I  now  propose  to  describe  some  of  the  meth- 
ods, that  have  been  employed  with  advantage, 
in  experiments  with  this  view, 
strength  of     92.   The  strength  of  mortars  may  be  consid- 

mortars  to  ~  ■> 

be  consid-  ered,  with  reference,  first,  to  their  resistance  to  a 

ered  under  ,    .  .     ,  '  ,.  .       . 

four  points  crushing  weight;  secondly,  to  their  resistance  to 
a  force  of  fracture  ;  thirdly,  to  their  adhesiveness  ; 
and  fourthly,  to  their  hardness. 
The  first       93.  If  we  confined  ourselves  to  experiments 
PquYry0noT  indicated  by  the  first  head,  it  would  not  be  easy 
al°cieent.ffi'  to  arrive  at  a  correct  estimate  of  their  compar- 
ative strength.      For,  if  prisms  of  the  different 
mortars    were    loaded    with    weights,    as    some 
direct,    until    they    were    actually    crushed,    it 
would    be    difficult    to    determine    the    moment 
when  they   began   to   give   way,   as  the   angles 
often   break    before    the    centre,    and    it    is   not 
clearly  seen,  when  the   substance  under  exam- 


RESISTANCE    OF    MORTARS.  •      53 

ination  has  really  yielded  to  the  load  *  It  may, 
therefore,  be  well  to  limit  the  examination  to  the 
three  latter  points  of  inquiry,  indicated  in  the 
preceding  Article  :  and  I  will  at  once  proceed  to 
describe  the  method  employed  by  Treussart  and 
Pasley,  in  measuring  the  resistance  of  mortars  to 
a  fracturing  force. 

94.  A  convenient  form  to  give  the  specimens  Mortars  to 

-  .  t      t     r  ■  •         1  /•      1         De  moulded 

oi  mortar  intended  lor  experiment,  is  that  01  the  into  prisms, 
parallelopiped,  into  which  they  may  be  easily 
moulded  by  means  of  a  box  of  the  proper  dimen- 
sions, say  six  inches  long,  three  inches  wide, 
and  three  inches  deep.  (Fig.  1.)  Having  fixed  piatei. 
the  proportions  of  the  mortars  to  be  tested,  the 
lime  or  cement  may  be  measured  in  the  state  of 
paste,  as  this  mode  is  ordinarily  pursued  in  prac- 
tice. The  cementing  matter,  whatever  it  may 
be,  being  then  added  to  the  sand  or  other  sub- 
stance, which  should  in  every  experiment  be 
carefully  measured  in  the  same  manner,  the  whole 
may  be  brought  to  the  requisite  temper,  by  pass- 
ing it  seven  or  eight  times  under  the  trowel.  The 
mortars  being  thus  made,  and  all  of  the  same 
consistence,  should  then  be  put  into  the  prism 
mould,  and  every  specimen  subjected  to  the  pres- 
sure of  the  same  weight,  say  six  hundred  pounds. 
When  the  mortars  have  stiffened  sufficiently,  they 
may  be  taken  from  the  mould,  and  set  aside, 
either  in  water  or  in  the  air,  until  it  is  desired  to 
submit  them  to  experiment.  It  sometimes  hap- 
pens that  the  exterior  of  the  prisms  is  harder  than 
the  interior,  while  at  other  times  the  contrary 
obtains.  For  this  reason,  it  was  Gen.  Treussart's 
custom  to  cut  off  with  a  chisel  about  half  an  inch 
from  each  side,  in  order  to  remove  every  part  that 
had  a  different  hardness  from  the  interior. f 

*  Totten's  Treussart,  p.  17.  t  Totten  on  Mortars,  p.  17,  252. 

5* 


54  TREATISE     ON    MORTARS. 

Mode  of  95.  The  prisms  having  attained  the  age  de- 
the^prisms. sired,  their  comparative  strength  maybe  ascer- 
tained by  breaking  them  down  with  weights 
applied  to  the  middle  of  each  prism,  which  is 
supported  at  the  ends,  during  the  operation,  by  a 
couple  of  iron  stirrups,  placed  at  the  clear  dis- 
tance of  some  four  inches  apart.  A  convenient 
Plate  i.  apparatus  for  this  purpose  is  shown  in  Fig.  2. 
Before  the  mortar  is  placed  upon  the  stirrup 
bearers,  another  iron  stirrup,  inverted,  is  passed 
over  one  end,  as  far  as  the  middle  of  the  prism. 
The  top  of  the  stirrup  thus  rests  upon  the  upper 
surface  of  the  prism,  while  to  its  bottom,  which 
is  open,  is  then  hooked  on  a  light  scale-board, 
upon  which  the  weights  are  placed,  and  gradu- 
ally increased  until  fracture  takes  place. 
Further  de-  96.  That  part  of  the  surface  of  the  two  sup- 
8t:hePappar0-f porting  stirrups,  upon  which  the  prism  of  mor- 
atus.  j.ar  rests,  is  flat,  while  the  inverted  stirrup  rest- 
ing on  the  top  of  the  prism,  has  the  form  of  a 
blunted  knife  edge  (Fig.  A.  e).  The  stirrups  and 
scale-board  are  suspended  under  a  gin  (or  triangle 
for  supporting  weights)  by  means  of  ropes,  or 
rods  of  iron,  though  the  cap  of  a  large  trestle,  or 
a  beam  sufficiently  strong  to  support  the  appar- 
atus, may  be  substituted  in  place  of  the  gin 
(Fig.  2,  B).  If  the  scale-board  be  too  small  to 
hold  the  necessary  weights,  we  may  place  upon 
it  a  couple  of  three  inch  planks,  which  may  then 
be  loaded,  from  the  centre  outwards,  by  two  or 
three  parallel  rows  of  weights,  as  the  case  may 
require.  (Fig.  2.) 
Form  for  97.  As  soon  as  fracture  takes  place,  the  break- 
'SesnJta!6  ing  weight,  including,  of  course,  the  weight  of 
the  scale  pan  and  its  appendages,  should  be  re- 
corded in  some  convenient  table  like  the  follow- 
ing, which  will  show  immediately  the  results 
obtained  by  mixing  different  sorts  of  lime   or 


RESISTANCE    OF    MORTARS. 


55 


cement  with  various  proportions  of  gravel,  sand, 
or  both.* 


When 
made. 

No.  of 
Exper- 

Lime  or  cement 

paste,  mixed 

with  G  (gravel), 

S  (coarse  sand), 

s  (fine  sand). 

If  kept 
under 

Age 

when 

broken, 

in  days. 

Proportion  of 
paste  to 

Frac- 
turing 
weight 

in 
pounds. 

ago   when 
immersed. 

Sand. 

Gravel 
and 
sand. 

Compact. 

1833. 
May  7. 

1 

Rich   lime   (Smith- 
field),  1  S  2. 

50        1  to  2 

164  1-2 

98.  A  common  method  of  comparing  the  adhe- 
siveness of  different  mortars  is  to  stick  bricks 
together  with  each  mixture,  in  rows  projecting 
from  the  side  of  a  brick  wall.  Before  commenc- 
ing one  of  these  rows,  a  small  rectangular  portion 
of  the  wall,  sufficiently  large  to  receive  the  first 
brick,  should  be  well  scraped,  and  the  joints  of 
the  brick-work  carefully  raked  out  for  about  half 
an  inch  in  depth.  The  wall,  thus  prepared,  must 
now  be  plastered,  and  its  joints  completely  filled 
with  mortar,  and  the  first  brick  should  be  at  once 
applied,  before  the  mortar  in  the  joints  has  be- 
come at  all  stiff.  Whenever  a  new  brick  is  to 
be  added,  it  is  well  to  immerse  it  in  water  for 
half  a  minute,  and  to  wet  also,  with  the  aid  of  a 
brush,  the  face  of  the  wall  or  brick  to  which  it 
is  to  be  attached.  The  mortar  should  then  be 
carefully  applied  to  both  surfaces  ;  first  in  a  thin 
coat  to  the  wall  or  brick  already  in  place,  and 
then  in  a  thicker  coat  to  the  new  brick,  and  the 
two  should  now  be  joined  together,  mortar  to 
mortar,  and  well  pressed  for  some  fifteen  or 
twenty  minutes.  No  new  brick  ought  to  be 
added  until  the  mortar  of  the  preceding  one  has 
become  perfectly  set.f 


Mode  of 
estimating 

the  adhe- 
siveness ot 

mortars. 


*  Pasley,  pp.  112,  131,  134. 


t  Pasley,  p.  108. 


OD  TREATISE     ON    MORTARS. 

Ve'sfof"  "■  The  method  just  described  is  best  adapted 
hydraulic  for  testing  the  adhesiveness  of  quick  setting  mix- 
tures,  and  affords  a  simple  and  striking  illustration 
of  the  uncommon  qualities  of  hydraulic  cement 
in  that  respect.  Capt.  Smith,  the  translator  of 
Vicat,  mentions  an  instance  in  which  33  bricks 
have  been  thus  successfully  supported.  Now, 
if  the  weight  of  the  brick  and  its  corresponding 
joint  regarded  as  homogeneous,  be  assumed  to 
be  six  pounds,  and  their  thickness,  when  the 
bricks  are  joined  together,  in  the  way  before- 
mentioned,  in  which  the  longest  dimension  is 
placed  vertical,  at  2£  inches,  then  the  strain  upon 
the  first  joint  would  be  equivalent  to  that  pro- 
duced by  a  weight  of  G534  pounds,  suspended 
at  the  centre  of  gravity  of  the  first  brick.* 
Adhesive-  100.  But  the  extraordinary  strength  of  pure 
hydraulic  cement  is  proved,  in  a  more  wonderful  man- 
Thernius-" ner,  by  two  semi-arches,  built  for  experiment  by 
tnted.  ]y[r  Brunei,  near  the  entrance  of  the  Thames 
tunnel.  This  arrangement  is  so  ingenious,  and 
will,  probably,  be  found  hereafter  of  so  much 
value  in  practical  architecture,  that  it  may  be 
well  to  describe  it,  though  not  strictly  in  keeping 
with  my  plan.  The  arches  spread  out  from  the 
same  common  central  pier  (like  two  branches 
from  different  sides  of  a  tree),  one  60  feet,  the 
other  about  37  feet  long,  the  rise  of  the  former 
being  10i  feet,  and  that  of  the  latter  about  10 
feet,  and  at  the  extremity  of  this  last  was  sus- 
pended a  weight  of  62,700  lbs. 

Two  views  of  these  semi-arches  are  shown  in 

Plate  i.    Figs.  3  and  4.    The  pier  from  which  they  sprang, 

measured  in  extreme  length,  10  feet,  and  in  width, 

4  feet  (the  last  only  appearing  in  elevation),  and 

*  Smith's  Vicat,  p.  112. 


RESISTANCE    OF    MORTARS.  57 

its  extreme  height  above  the  ground  was  8  feet. 
The  arches  were  13  inches  in  depth  or  thickness, 
and  3  feet  6  inches  wide,  and  the  cornice,  with 
which  the  one  coincided,  and  the  other  nearly 
so,  at  their  outward  extremities,  was  also  of  the 
same  width.  The  width  of  the  brick-work, 
however,  in  the  spandrels,  or  intermediate  spaces 
on  each  side  of  the  central  pier,  above  the  spring 
of  each  semi-arch  and  below  the  cornice,  and 
within  the  openings  of  the  seven  small  arches, 
which  projected  on  one  side  about  a  foot  from 
the  spandrels,  was  only  18  inches. 

The  brick-work  was  bonded  with  10  tiers  of 
3  wooden  laths  each,  commencing  at  the  height 
of  4£  feet  above  the  ground,  and  laid  horizontally 
in  the  joints  of  the  spandrel  courses.  Above 
these  it  was  bonded  with  12  tiers  of  hoop  iron, 
also  laid  horizontally  in  the  joints  of  the  remain- 
ing courses  of  the  spandrels,  and  in  those  of  the 
cornice,  in  the  following  order  as  to  number,  viz.  ; 
in  the  lowest  joint  two  pieces  of  hoop  iron,  in 
the  second  3,  in  the  third  4,  in  the  fourth  5,  in 
the  fifth,  sixth,  seventh,  eighth  and  ninth,  each  6, 
in  the  tenth  4,  in  the  eleventh  6,  above  which 
one  more  course  of  bricks  completed  the  whole 
height.  Now  although  much  must  be  ascribed 
to  the  pieces  of  hoop  iron  introduced  horizontally 
into  the  joints,  inasmuch  as  cement  alone  can 
only  support  a  certain  limited  number  of  bricks ; 
still,  unless  it  had  the  property  of  setting  almost 
instantaneously,  and  uniting  the  brick-work  into 
a  solid  mass,  the  hoop  iron,  of  itself,  could  give  but 
little  stability  to  a  structure  thus  suspended  in  air.* 

101.  The  method  of  testing  different  mortars    second 
and  cements  by  setting  out  bricks  from  the  side  teSttagad- 
of  a  wall,  though  very  easy  of  application,  some-  hesiveness- 

*Pasley,p.  39,  116. 


58  TREATISE    ON    MORTARS. 

times  leads  to  doubtful  results,  if  executed  by 
different  persons  in  a  different  manner,  or  in  dif- 
ferent states  of  the  weather.  A  better  method  is 
to  employ  the  breaking-down  apparatus  before 
described,  consisting  of  the  scale-board,  planks 
and  weights,  and,  in  addition,  a  couple  of  pairs 
of  nippers  to  be  used  with  the  gin,  or  other  suit- 
able means  of  suspending  the  apparatus.  In  place 
of  bricks,  Gen.  Pasley  recommends  a  number  of 
pieces  of  any  sound,  hard  stone,  each  10  inches 
long,  4  inches  broad,  and  about  4  inches  thick, 
and  furnished  with  mortises  in  the  sides.  These 
mortises  are  each  one  inch  wide,  one  inch  deep, 
and  from  £  to  half  an  inch  in  height,  and  should 
have  at  least  2J-  inches  of  solid  stone  above  and 
below  them.  They  are  intended  to  receive  the 
nippers,  after  the  stones  have  been  cemented  in 
piate  i.  pairs,  as  shown  in  Fig.  5.  The  rectangular  sur- 
face of  the  stone,  where  the  mortar  is  to  be 
applied,  should  be  well  roughened,  and  all  the 
surfaces  made  as  nearly  alike  as  possible.  The 
joint  should  be  about  ■§  of  an  inch  thick,  and  in 
order  that  the  mortar  may  be  equally  consolidated 
in  every  case,  it  is  well  to  subject  each  set  of 
stones  to  the  pressure  of  some  600  lbs.  for  five 
minutes  after  they  are  joined  together. 

The  mortars  experimented  upon  should  have 
ample  time  to  set,  before  the  breaking-down 
apparatus  is  applied,  and  the  trials  with  each 
specimen  should  be  multiplied  as  far  as  conve- 
nience will  permit. 

The  little  blocks  of  stone,  if  cleaned  after  each 
experiment,  may  be  used  for  years  with  advan- 
tage. We  have  only  to  make  the  nippers  and 
mortises  fit  rather  tightly,  and  to  prevent  the 
stones  from  falling  to  the  ground,  when  the  joint 
is  fractured.* 

*  Pasley,  pp.  126,  127. 


RESISTANCE    OF    MORTARS. 


59 


When  stones  cannot  be  obtained  without  in- 
convenience, bricks  may  be  substituted  in  their 
place,  the  nippers  being  slightly  modified. 

102.  The  following  table  from  Gen.  Pasley's  £°™<X; 
work  on  mortars,  shows  the  comparative  cohesive      sive,    ,. 

/.  .  strength  of 

strength  of  pure  cement,  01  cement,  mixed  with   pureee- 
sand,  and  of  common  chalk  lime  mortar.* 


Weight 

Average 

No.  of 
Experiment. 

Whether  with  cement  or  with 
chalk  lime. 

Age  in  days 
or  years. 

that  tore 

the  joint 

asunder, 

in  lbs. 

fractur- 
ing 
weight 
in  lbs. 

1 

Pure  cement, 

11  days. 

1241) 

» 

2 

It             « 

17    " 

10113  } 

1092 

3 

((            it 

17    " 

1031  ) 

1 

Cement  1,  sand  1, 

11     " 

205) 

2 

CI                       It 

11    " 

2.57  } 

258 

3 

ti                     It 

17    " 

313) 

1 

Ordinary  mortar,   fat  lime, 

30  years. 

3341 

2 

CI                   It                 It          u 

30    « 

64  1 

3 

4 

IC                   IC                  II          IC 

30    " 
30    " 

75  1 
47  f 

155 

5 

II              II             It        II 

30    " 

205  1 

6 

t<                   II                  II          II 

30    <S. 

204  J 

It  appears  from  the  table,  that  pure  cement  is 
four  times  as  strong  as  a  mixture  of  cement  and 
sand  in  equal  proportions,  though  the  latter,  when 
only  eleven  days  old,  has  more  cohesive  strength 
than  ordinary  mortar,  which  has  attained  the 
age  of  thirty  years. 

103.  Table  showing  the  comparative  adhesive- 
ness of  hydraulic  cement  to  brick  and  stone.f 


.Materials  used  in 
experiments. 

No.  of  experi-   [Age  of  cement  in 
ments.                        days. 

Average  fractur- 
ing weight  in  lbs. 

Bricks. 

Sand  stone. 
Granite. 

12 
5 
5 

11  to  13 

11 

11 

1359 
1349 
900 

*  Pasley,  pp.  126,  127. 


t  Pasley,  p.  123. 


60  TREATISE    ON    MORTARS. 

Hardness  of     104.  The  hardness  of  different  mortars  was 
i™ w  bso-  compared  by  Col.  Totten,  in  his  experiments  at 

mated.  port  AdamSj  by  ascertaining  the  weights  applied 
on  a  circular  plane  surface  of  0.16  of  an  inch  in 
diameter,  or  .020  of  an  inch  area,  which  each 
specimen  under  trial  will  support.     The  mode  of 

piatc  i.  experiment  is  represented  in  Fig.  6.  The  circular 
surface  at  the  extremity  a  presses  upon  mortar 
adhering  to  a  brick.  The  arms  of  the  lever  b  are 
of  equal  length,  so  that  the  upward  force  at  c  is 
equal  to  the  pressure  at  a.* 

A  specimen  of  hydraulic  cement  from  the 
State  of  New  York,  five  months  after  being  made 
into  paste,  yielded  only  to  a  weight  of  1053  lbs. 
when  tested  in  the  above  described  manner. 
Kemarks.  105.  By  applying  the  methods  of  determining 
the  resistance  of  mortars,  described  in  this  chap- 
ter, to  the  various  materials  at  his  command,  each 
constructor  can  determine  for  himself,  in  every 
case,  the  proportions  of  ingredients  best  calcu- 
lated to  produce  good  results. 

*  Totten,  p.  232. 


FABRICATION    OF    LIMES.  61 


CHAPTER   V. 

ON  THE  FABRICATION  OF  LIMES,  ETC.  IN  THE 
LARGE  WAY. 

106.  When  the  constructor  is  under  the  neces-  Limestone 
sity  of  manufacturing  lime,  he  should  examine  t0e!with* 
all  the  quarries  in  his  vicinity,  and  test  carefully     CIire- 
specimens    from    each,  in    the    manner  recom- 
mended in  Chapter  I.      He  must  not  confine 
himself  to  a  single  fragment  of  stone  taken  at 
random,  but  should  try  several  from  the  same 
quarry  ;  and  when  the   strata  of  stone  are  not 
exposed  to  view,  shafts  should  be  sunk,  in  order 

to  seek  out  those  layers,  which  will  furnish  the 
best  materials.  It  may  be  observed,  in  general, 
that  the  stone  is  procured  from  the  quarry  by  the 
aid  of  hammers,  wedges,  levers,  and  even  by 
mining,  according  to  the  character  of  the  mineral 
deposit,  which  may  exist  in  mass,  or  be  arranged 
in  layers.* 

107.  The  mineral,  having  been  selected,  should  Remarks  on 
then  be  calcined  in  kilns  properly  constructed  for 

the  purpose.  The  object  of  the  calcination,  as 
remarked  in  another  place,  is  to  drive  off  the 
water  and  carbonic  acid,  and  during  the  operation 
the  stone  loses  from  one-half  to  one-third  of  its 
weight,  and  from  one  to  two-tenths  of  its  volume. 
The  action  takes  place  at  first  on  the  surface  of 
the  stones,  and  it  is  only  by  very  strong  heat  that 
their  central  parts  are  freed  from  the  water  and 

*  Raucourt,  p.  123. 

6 


62  TREATISE    ON    MORTARS. 

acid.  These  last,  too,  are  expelled  with  much 
more  facility  from  stones  newly  quarried,  than 
from  those  which  have  had  time  to  dry  ;  and  ex- 
perience has  farther  proved,  that  a  current  of  aque- 
ous vapor  facilitates  the  reduction  of  limestone 
into  lime. 

For  the  above  reasons,  it  will  be  advantageous 
to  reduce  the  mineral  to  small  fragments,  and 
sprinkle  these  with  water,  before  charging  the 
kiln,  throwing  a  few  buckets  of  water,  from 
time  to  time,  on  the  burning  faggots,  when 
wood  is  the  combustible ;  or,  if  we  are  burning 
coal,  it  will  be  well  to  place  a  large  vessel  of 
water  in  the  draught  of  air,  at  the  mouth  of  the 
kiln. 

The  agency  of  the  air  is  no  farther  necessary, 
than  as  it  operates  in  the  combustion  of  the  fuel, 
though  no  limestone  can  be  converted  into  lime, 
in  a  vessel  so  close  as  to  prevent  the  escape  of 
carbonic  acid.* 
Kilns.  108.  The  great  heat  to  which  all  kilns  are 
subjected,  renders  them  liable  to  premature  de- 
struction by  expansion.  For  this  reason,  as  well 
as  on  account  of  the  increased  facility  in  charging 
them,  they  are  usually  placed  on  the  side  of  a 
bank,  or  sometimes  under  ground,  in  order  that 
the  walls  may  be  strengthened,  as  much  as  pos- 
sible, against  the  tendency  outward.  When  they 
are  constructed  independently  of  any  such  sup- 
port, it  is  necessary  to  give  great  thickness  to 
the  walls,  support  them  by  counterforts,  or  bind 
them  together  by  bands  of  wood  or  iron. 

Lime  kilns  are  generally  constructed  with 
more  regard  to  the  nature  of  the  fuel  employed, 
than  to  the  qualities  of  the  mineral  to  be  calcined, 


*  Raucourtj  p.  123.— Smith's  Vicat,  pp.  13,  153. 


BURNING    OF    LIMESTONE.  63 

and  may  therefore  be  comprised  under  two  gen- 
eral heads :  the  "  Flare  or  Flame  Kiln,"  in  which 
wood  is  commonly  used  as  the  combustible,  and 
the  "  Perpetual  Draw-Kilns,"  which  are  generally 
intended  for  burning  with  coal.* 

109.  The  Flame-kiln,  represented  in  Fig.  1,  ££«"'. 
is  recommended  by  Col.  Raucourt,  as  one  of  the 

best  of  the  first  class.  The  form  of  the  interior 
is  that  of  an  egg,  somewhat  elongated,  and  the 
dimensions  indicated  in  the  figure,  are  those  sug- 
gested by  convenience  and  economy.  Like  all 
kilns,  it  should  be  lined  on  the  inside,  for  a  thick- 
ness of  twelve  or  fifteen  inches,  with  some  ma- 
terial, like  soap-stone  or  fire-brick,  capable  of 
resisting  strong  heat,  and,  as  an  additional  pre- 
caution, the  cement  used  in  constructing  this 
lining  should  be  clay,  or  some  argillaceous  earth, 
tempered  with  water.  The  door  of  the  kiln 
should  be  sheltered,  as  well  as  possible,  from  the 
action  of  the  wind,  and  a  shed  roof  is  sometimes 
placed  over  the  top,  to  protect  it  from  the  rain. 
When  this  latter  is  dispensed  with,  the  top  of  the 
kiln  may  be  covered  with  flat  stones,  cemented 
at  the  joints  with  clay,  sufficient  openings  being 
left  for  the  passage  of  the  smoke,  and  the  due 
activity  of  the  draught.* 

110.  The  operation  of  charging  the  kiln  is  cha»mg 
commenced  by  constructing  the  furnace  or  thek,In* 
dome  b,  with  the   largest  fragments  of  stone, 

and  filling  up  in  rear  of  them  with  smaller  pieces, 
but  leaving  space  enough  for  the  flame  to  circu- 
late freely.  The  height  of  the  furnace  should  be 
five-twelfths,  and  its  width  at  least  one-half  of 
the  greatest  breadth  of  the  interior  of  the  kiln. 
The  arched  dome  for  the  fire-place  being  com- 

*  Raucourtj  pp.  123,  130. 


ncm. 


64  TREATISE    ON    MORTARS. 

pleted,  the  larger  blocks  of  stone  (which  should 
not,  in  general,  exceed  half  a  cubic  foot  in  size) 
are  placed  nearest  the  furnace,  those  of  middling 
size  farther  off,  and  the  smallest  pieces  next  the 
sides  of  the  kiln,  in  order  that  the  burning  may 
be  as  uniform  as  possible. 

For  greater  convenience  in  removing  the  cal- 
cined stone  and  charging  the  kiln,  when  its 
dimensions  are  large,  a  small  door  p,  closed  dur- 
ing the  burning  with  stones  laid  in  clay,  is  some- 
times made  in  the  side  walls.* 

Meanaof       HI.  When  the  wood  burns  very  freely,  the 

Pcombu9-g  air,  which  enters  at  the  "  eye  "  or  mouth  of  the 
kiln,  is  sufficient  to  produce  an  active  combus- 
tion. If  the  fuel  requires  a  great  draught,  sev- 
eral air-holes,  s  s,  should  be  made  in  an  arch  v, 
placed  at  the  extremity  of  an  under-ground  pas- 
sage, w,  which  brings  the  air  from  the  exterior. 

Should  the  fire,  from  any  cause,  fail  to  heat 
equally  all  parts  of  the  interior,  logs  of  wood,  //, 
should  be  inserted  in  the  midst  of  those  stones 
which  are  apt  to  be  burned  imperfectly  ;  these 
logs,  upon  being  consumed,  leave  a  passage-way 
for  the  flames,  and  the  heat  is,  in  this  way,  dis- 
tributed more  uniformly. f 

Rectangu-       H2.  Flame-kilns  have  various  interior  forms; 

lime  and  that  just  described  is  perhaps  the  best,  though 
the  rectangular  prism  is  more  commonly  used. 

piateii.  The  rectangular  kiln  shown  in  Fig.  2,  is  often 
used  for  burning,  at  the  same  time,  both  lime- 
stone and  bricks.  It  is  usually  about  fifteen  feet 
high,  with  walls  from  four  to  five  feet  in  thick- 
ness. 

The  furnaces  of  flame-kilns  of  this  form,  con- 
sist, generally,  of  several  arched  openings  (the 

*  Raucourt,  pp.  123,  130.  t  Raucourt,  p.  132. 


BURNING    OF    LIMESTONE.  65 

number  varying  with  the  size  of  the  kiln),  which 
extend  from  front  to  rear,  and  are  arched  through- 
out with  large  pieces  of  the  limestone.  The 
mineral,  broken  into  fragments  of  half  a  cubic 
foot  or  less,  is  then  piled  up  to  the  height  of 
about  eight  feet  above  the  arches,  and  the  remain- 
ing interior  space  filled  with  some  fifteen  or 
twenty  thousand  unburned  bricks.  When  these 
kilns  are  to  be  fired,  small  quantities  of  the  fuel 
are  placed  under  the  arches,  and  the  external 
openings  are  then  bricked  up  nearly  to  the  top, 
only  sufficient  room  being  left  to  add  fuel  as 
occasion  may  require.* 

113.  "Field-kilns,"  of  cylindrical  form,  and  Te{JXsrary 
expeditious,   though  insecure,  construction,  are 
sometimes  employed  on  works,  where  much  lime 

is  consumed  in  a  short  time.  Fig.  3,  represents  Plate  n. 
a  kiln  of  this  kind.  Above  an  oven-shaped  vault, 
is  raised,  in  the  form  of  a  tower,  a  high  stack 
of  limestone  :  this  is  enclosed  with  earth,  well 
rammed,  and  supported  farther  by  a  coarse  wat- 
tling, in  which  an  opening  is  left  to  introduce 
the  fire  beneath  the  vault. f 

114.  Several  attempts  have  been  made  to  combina- 
economize  the  calcination  of  limestones,  by  the  coke-oven 
preparation,  at  the  same  time,  of  other  materials  witkif'!lI,e 
requiring  in  their  manufacture  the  action  of  heat. 

The  case  of  brick-burning  has  been  already  in- 
stanced, and  it  will  not  be  out  of  place  to  mention 
a  contrivance,  by  means  of  which  the  fuel  employ- 
ed is  saved,  almost  entirely,  by  being  converted 
into  coke.  It  is  a  combination  of  a  coke-oven  with 
a  lime-kiln,  invented  by  Mr.  Heathorn,  and  de- 
scribed by  the  patentee  as  follows:  %  "  The  draw- 
ing, Fig.  4,  represents  a  vertical  section  of  the  lime-   Plate  n 

*  Davy's  Constructive  Manual,  p.  127.  t  Vicat,  p.  15. 

t  Davy's  Constructive  Manual,  p.  124. 

6* 


66  TREATISE    ON    MORTARS. 

shaft  and  coke-ovens.  AA  are  the  side-walls 
(about  four  feet  in  thickness)  of  a  rectangular 
tower,  filled  with  the  limestone,  which  is  raised 
to  the  top  in  a  box,  by  means  of  convenient 
tackle.  The  coke-ovens,  varying  in  number  ac- 
cording to  the  magnitude  of  the  kiln,  are  arranged 
in  connection  with  the  shaft,  in  the  same  manner 
as  the  two  represented  at  FF.  They  are  sup- 
plied with  coal  through  doors  in  the  front  walls 
(not  seen  in  the  section),  and  there  is  a  long  and 
narrow  slit  in  the  upper  part  of  the  doors,  for  the 
admission  of  sufficient  atmospheric  air,  to  cause 
the  combustion  of  the  inflammable  part  of  the 
coal.  The  flames  pass  into  the  shaft  through  a 
series  of  flues  (two  of  which  are  shown  at  GG), 
and  the  draughts  from  either  side  are  prevented 
from  interfering  with  each  other,  by  means  of 
the  partition  wall  H,  which  directs  the  course  of 
the  flame  throughout  the  whole  mass  of  the  inte- 
rior. 

When  the  kiln  is  completely  charged  with 
lime,  the  openings  77,  in  front,  or  beneath  the 
iron  bars  BB,  are  closed  with  bricks  and  an  iron- 
cased  door,  filled  on  the  inside  with  sand,  to 
exclude  the  air  and  prevent  the  loss  of  heat. 
Therefore,  while  the  burning  is  going  on,  no 
air  is  admitted,  except  through  the  narrow  aper- 
tures before-mentioned,  in  the  coke-oven  doors. 
When  the  calcination  of  the  limestone  is  com- 
pleted, the  barricades  at  II  are  removed,  and  the 
iron  bars  BB  drawn  out.  The  lime  then  falls 
down,  and  is  removed  with  the  aid  of  wheel- 
barrows. If  the  lime  cakes  or  arches  itself,  so 
that  it  does  not  readily  fall,  a  hooked  iron  is  em- 
ployed to  bring  it  down.  In  order  to  facilitate 
this  operation,  openings  closed  by  iron  doors,  two 
of  which  are  brought  into  view  at  KK,  are  made. 


the  burn- 
ing. 


BURNING    OF    LIMESTONE.  67 

at  convenient  distances,  from  the  top  to  the  bot- 
tom of  the  shaft.  Two  similar  apertures  are 
shown  in  the  coke-ovens  at  LL,  for  the  conve- 
nience of  clearing  out  the  lateral  flues  GG,  from 
any  matter  that  might  obstruct  the  free  passage 
of  the  flame  or  heated  air.  When  the  coals  have 
been  reduced  to  coke,  the  oven-doors  (not  repre- 
sented) are  opened,  and  the  product  removed  with 
convenient  instruments.* 

115.  In  all  flame-kilns,  the  burning  is  com-  Conduct  of 
menced  with  a  small  fire,  which  is  kept  at  an 
uniform  temperature,  from  twelve  to  forty-eight 
hours.  The  object  of  this  is  to  drive  off  gradu- 
ally the  moisture  contained  in  the  mineral,  as  the 
safety  of  the  kiln  would  be  endangered  by  the  ex- 
plosions, that  might  otherwise  take  place.  When 
the  stones  become  dry,  they  assume  a  black  hue 
from  contact  with  the  smoke,  and  will  then  bear 
a  slight  increase  of  heat,  which  however  should 
remain*  uniform,  until  the  smoke  is  wholly  con- 
sumed. At  this  stage,  the  furnace  may  be  filled 
with  the  combustible,  and  the  fire  thus  increased 
to  its  highest  heat,  which  is  kept  up  until  the 
calcination  is  complete.     (Art.  15.) 

The  time  required  for  the  burning  varies  with 
a  multitude  of  circumstances,  the  character  of 
the  fuel,  the  quality  of  the  stone,  the  direction  of 
the  wind,  &c.  &c,  and  can,  therefore,  be  ascer- 
tained only  from  practical  experience.  Burners 
usually  decide  from  the  general  settling  of  the 
charge,  which  varies  from  one-fifth  to  one-sixth, 
the  color  of  the  flame  at  the  top  of  the  kiln  (an 
indistinct  pale  yellow),  and  the  glowing  red  or 
rosy  white  hue  of  the  interior  mass.f 


*  Davy's  Constructive  Manual,  p.  124. 
t  Raucourt,  p.  134. 


68 


TREATISE    ON    MORTARS. 


PERPETUAL    DRAW-KILNS. 


irfinrn«lda'  ^^'  ^  common  form  of  coal -kilns  is  that  em- 
Yorkshire,  ployed  in  Yorkshire,  England,  the  elevation, 
Plate  in.  plan  and  section  of  which  are  shown  in  Figs.  5, 
6,  7,  respectively.  The  side  of  the  hill,  near  the 
rock  from  which  the  limestone  is  taken,  is  usually 
chosen  as  the  place  for  building  the  kiln,  and 
operations  are  commenced  by  excavating  the 
bank  to  a  sufficient  depth  to  receive  the  back  of 
the  structure.  The  shaft  is  lined  with  a  facing, 
twelve  or  eighteen  inches  thick,  of  some  material 
that  will  resist  the  action  of  fire,  and  enclosed 
with  two  separate  walls,  the  space  between  which 
is  filled  with  small  rubble  or  sand,  to  obstruct  the 
passage  of  the  heat.* 

117.  Perhaps  the  most  ordinary  form  of  per- 
petual kilns,  is  that  of  the  inverted  cone.  Figs. 
8,  9,  10,  exhibit  a  very  convenient  one  of  this 
shape,  used  for  burning  hydraulic  cement  at 
Sheerness  dock-yard.  Its  exterior  presents  the 
appearance  of  a  cylindrical  tower,  seventeen  feet 
in  external  diameter,  and  twenty-one  and  a  half 
feet  in  extreme  height.  The  hollow  inverted 
conical  frustrum,  forming  the  interior  of  the  kiln, 
has  a  diameter  of  eight  feet  at  top,  and  five  and 
a  half  feet  at  bottom.  It  is  enclosed  by  a  nine- 
inch  ring  of  brick-work,  which  is  surrounded  by 
brick-work  in  mass.  Beneath  it  is  a  small  dome, 
two  feet  three  inches  high,  to  throw  aside  the 
calcined  cement  which  falls  down  through  the 
ash-holes  of  four  openings  or  "eyes,"  formed  in 
arched  recesses  at  the  bottom  of  the  kiln.  These 
recesses  increase  by  splays  and  gathering  courses, 
from  more  moderate  dimensions  near  the  inside 


Conical 
coal-kilns. 


Plate  III. 


*  Davy's  Constructive  Manual,  p.  130. 


BURNING    OF    LIMESTONES.  69 

to  six  feet  three  inches  by  seven  feet  six  inches 
(extreme  width  and  height)  at  the  outside.  The 
ash-holes  are  two  feet  six  inches  wide,  and  eight- 
een inches  high,  to  the  crown  of  the  flat  arch 
which  covers  them ;  and  within  the  recesses,  at 
an  interval  of  fifteen  inches  above  the  ash-holes, 
are  openings  for  supplying  the  requisite  draught 
of  air,  twelve  inches  square,  and  having  iron  bars 
at  top  to  support  the  brick-work  over  them.  To 
guard  against  accidents  to  the  workmen,  employ- 
ed in  charging  the  kiln,  the  tower  is  provided 
with  a  wooden  fence  on  the  top ;  and  it  is 
strengthened  againt  the  expansive  force  of  the 
fire  by  four  wrought  iron  hoops,  enclosing  the 
brick-work,  each  three  inches  wide  and  three 
eighths  of  an  inch  thick. 

The  kiln  just  described  is  represented  as  pro- 
vided with  four  openings,  though  more  usually, 
conical  kilns  have  but  one,  as  shown  in  Fig.  11.  piateiv. 
Vicat  recommends  an  improvement  of  this  in- 
terior form,  and  would  substitute  those  seen  in 
Figs.  12,  13,  as  answering  perfectly.*  piateiv. 

118.  In  perpetual   kilns,   the    charge   usually  Manner  of 
rests  upon  iron  bars  placed  at  the  bottom.     The  pCehrpegtuai 
process    of  filling  the    kiln   is   commenced,   by     kllD3, 
placing  a  layer  of  wood  and  shavings,  about  a 
foot  thick,  upon  the  grating  :  over  this  first  layer, 
is  then  placed  a  layer  of  the  lime-stone  (broken 
into  pieces  of  the  size  of  the  fist)  surmounted  by 
a  layer  of  coal,  each  of  the  last  two  varying  in 
thickness  according  to  the  nature  of  the  mineral. 
The    pure    lime-stones  require   strong    heat    for 
their  calcination  :  the  hydraulic  lime-stones  fuse 
readily,  and  the  more  so,  as  they  contain  more 
of   the    hydraulic    principle.     In    preparing  fat 

*  Pasley,  p.  283.— Vicat,  p.  13. 


70  TREATISE    ON    MORTARS. 

lime,  therefore,  the  layer  of  stone  should  be  only 
six  to  eight  inches  thick ;  in  preparing  hydraulic 
cement,  its  thickness  may  equal  fourteen  inches. 
The  layer  of  coal  required  with  the  former  has 
usually  one-third  of  the  thickness  of  the  stratum 
of  lime-stone  :  with  the  latter,  the  coal  occupies 
but  little  more  space,  than  that  necessary  to  level 
off,  and  fill  up  interstices  in  the  stone.  Alternate 
strata  of  the  stone  and  coal  are  then  laid,  until 
four  or  five  are  in  place.  The  fire  is  now  light- 
ed, and  as  soon  as  it  makes  its  appearance  above 
the  upper  stratum,  the  workmen  commence  anew 
to  charge  the  kiln,  and  continue  the  operation 
until  it  is  completely  filled.  The  layers,  how- 
ever, are  placed  pari  passu  with  the  progress  of 
the  fire,  in  order  to  avoid  the  necessity,  in  case 
it  should  be  extinguished,  of  unloading  the  whole 
charge ;  and  the  calcination  may  consequently 
be  completed  in  the  lower  part  before  the  kiln  is 
entirely  full.  As  soon  as  the  fire  goes  out  below 
and  the  calcined  product  becomes  cold,  the  iron 
grating  is  removed,  and  the  material  carried  off, 
in  order  that  the  air  may  circulate  more  freely, 
and  the  mass  undergoing  combustion  may  be  as 
large  as  possible.  The  operations  of  charging 
the  kiln  and  removing  the  lime,  may  now  go 
on  simultaneously,  as  long  as  may  be  neces- 
sary.* 
Remarks  on  119.  Both  kinds  of  kilns  are  employed  for 
kilns.  Durning  au  the  varieties  of  lime-stone.  The 
flame-kilns  require  less  experience  for  the  proper 
conduct  of  the  burning,  and  therefore  usually 
give  the  best  results  ;  but  they  are  not  so  econom- 
ical as  the  perpetual  kilns,  when  coal  is  employed 
as  the  fuel,  and  the  burning  goes  on  without  in- 
terruption. 

*  Raucourt,  p.  148. 


BURNING    OF    LIMESTONES.  71 

120.  The  pure  limestones  sustain  a  white  heat  ^™°turnetI7U°f 
without    inconvenience;    the    compound    lime-    latedby 

.  /»      i  •    •  nature  of 

stones,  with  the  proportions  of  clay  requisite  to  mineral. 
afford  hydraulic  lime  or  hydraulic  cement,  are 
easily  over-burned,  and  therefore  require  great 
care  in  their  calcination.  The  heat  should  never 
be  increased,  in  burning  the  latter,  beyond  a  red 
heat,  and  the  diminution  of  intensity  may  be 
made  up  by  duration. 

When  fat  lime  is  not  sufficiently  burned,  it 
either  does  not  slake  at  all,  or  only  partially, 
leaving  a  solid  kernel,  or  subcarbonate  with  an 
excess  of  base. 

When  the  hydraulic  varieties  are  not  burned 
enough,  they  slake  with  great  difficulty,  more 
usually  not  at  all,  and,  if  pulverized,  furnish  a 
powder  altogether  inert.  This,  too,  is  the 
character  of  the  product  when  too  much  burnt, 
besides  exhibiting  a  dark  color  not  natural  to  the 
limestone,  and  being  covered  with  a  kind  of 
enamel  about  the  angular  parts.* 

121.  I  learn  from  Mr.  White  (a  large  manu-  Manufec- 
facturer  of  Rosendale   cement,  in  the   State  of    drauiic 
New  York,  to  whom  I  am  iddebted  for  interest-  thTunited 
ing  information  on  this  subject),  that  both  the    states- 
flame  and  perpetual  kilns  have  been  employed  at 

his  works,  for  burning  the  cement  stone.  He 
recommends  the  use  of  the  former,  if  regard  be 
had  simply  to  the  quality  of  the  product ;  but  the 
latter  is  commonly  preferred,  as  possessing  great 
advantages  on  the  score  of  economy.  In  general, 
the  kilns  for  calcining  this  kind  of  limestone 
differ  from  the  ordinary  lime-kilns  in  having 
walls  somewhat  thicker,  and  more  compactly 
built,   in   order  that  the  ignited  mass  may  be 

*  Smith's  Vicat,  pp.  13,  14. 


72 


TREATISE    ON    MORTARS. 


secured  from  contact  with  cold  air,  which  is 
found  to  exert  an  injurious  influence.  The  per- 
petual kiln,  employed  for  the  purpose  in  the 
United  States  (I  infer  from  the  description),  is 
not  unlike  the  Yorkshire  kiln  (Figs.  5,  6,  7, 
Plate  III),  and  the  siftings  of  anthracite  coal, 
obtained  at  small  cost  from  the  coal  yards,  have 
been  found  to  answer  well  as  the  combustible. 

When  a  kiln,  similar  to  that  represented  in 

Plate  in.  Figures  5,  6,  7,  is  to  be  constructed,  Mr.  White 

recommends  one  of  ten  feet  interior  diameter, 

and   thirty   feet    entire    depth,    as   being    more 

economical  than  one  of  less  size. 

In  using  the  flame-kiln,  it  would  not  be  safe 
to  construct  the  fire-arches  with  the  hydraulic 
limestone,  as  it  fuses  easily,  and  is  moreover  apt 
to  explode  under  the  action  of  fire ;  but  as  or- 
dinary limestone  bears  a  white  heat,  this  latter 
may  be  substituted  for  the  purpose,  with  advan- 
tage. The  fire-arches  being  completed,  the  kiln 
is  filled  with  fragments  of  cement  stone,  varying 
in  weight  from  half  a  pound  to  twelve  pounds, 
and  the  charge  rounded  off  above,  its  centre  being 
some  three  or  four  feet  above  the  top  of  the 
masonry.  A  moderate  fire  is  employed  at  first, 
in  order  to  dry  the  interior  mass  gradually,  as 
explosions  would  otherwise  take  place  to  the 
injury  of  the  kiln,  and  the  broken  stones  would 
be  fused  at  the  surface,  before  their  central  parts 
were  properly  calcined.  When  the  moisture  has 
been  driven  off,  which  usually  requires  about 
thirty  hours,  the  fire  is  increased,  and  kept  up 
until  the  whole  charge  has  been  brought  to  a  red 
heat.  At  this  stage,  the  top  of  the  kiln  is  covered 
with  flat  stones,  cemented  with  mud  or  mortar, 
and  left  to  cool  for  two  or  three  days,  when  the 
door  and  arches  are  taken  down,  and  the  removal 


BURNING    OF    LIMESTONE,  73 

of  the  hydraulic  cement  commenced.  Great  care 
is  now  requisite  in  selecting  only  the  good  mate- 
rial, and  rejecting  all  the  common  lime,  the  stone 
which  has  not  been  burned  enough,  and  that 
which  is  fused  or  too  much  burned.  The  cement 
of  proper  quality  is  then  taken  to  the  mill,  where 
it  is  first  broken  into  pieces  proper  for  grinding, 
by  a  machine  resembling  a  "Gypsum  Cracker," 
and  afterwards  reduced  to  an  impalpable  powder 
by  the  action  of  the  mill-stone. 

122.  Two  modes  of  grinding  and  sifting  hy-    ^"f^ 
draulic  cement  are  employed  in  England.     The  ami  sifting 
first  differs  in  nothing  from  the  method  of  grind-  England. 
ing  wheat  and  sifting  the  flour,  the  same  sort  of 
hoppers,  mill-stones,  and  bolting  apparatus  being 
used  in  either  case.     In  the  other,  the  cement  is 
reduced  to  powder  under  the  wheel  (weighing 
upwards  of  two  tons)  of  a  grinding-mill,  worked 
by  horse  power  and  resembling  the  mortar-mill 
to    be   described   hereafter.     The    powder    thus 
obtained  is  then  passed  through  a  sieve,  having 
seventeen  wires  to  the  lineal  inch,  and  afterwards 
packed  in  casks  or  sacks  for  use,  while  the  coarser 
parts,  retained  by  the  sieve,  are  thrown  under  the 
wheel  to  be  ground  anew.* 

]  23.  It  was  mentioned  in  a  preceding  chapter,  storing 
that  the  qualities  of  hydraulic  cement  which  has  °f  damaged 
been  damaged  by  exposure  to  the  air,  may  be    cement- 
restored  by  a  new  burning.     When  any  consider- 
able quantity  is  to  be  recalcined,  it  will  be  found 
convenient  to  knead  it,  by  the  addition  of  water, 
into  lumps  of  some  size,  before  placing  it  in  the 
kiln.     When  it  has  not  sufficient  coherence  to 
hold  together  of  itself,  a  small  proportion  of  clay, 
not  exceeding  one  tenth,  may  be  mingled  with 
it,  without  material  injury  to  the  product. 

*  Pasley,  p.  285. 


74  TREATISE    ON    MORTARS. 


ARTIFICIAL    HYDRAULIC    CEMENT. 

Artificial  124.  When  the  natural  cement  is  only  to  be 
cement0  had  at  great  cost,  it  may  become  necessary  to 
twowa/s.  manufacture  an  artificial  hydraulic  cement.  This 
may  be  done  in  two  ways,  and  the  result  obtained 
by  either  process,  if  the  materials  are  properly 
selected,  may  be  equal,  if  not  superior,  to  the 
natural  product. 

The  most  perfect,  but  the  most  expensive 
method,  is  to  mingle  rich  lime,  which  has  been 
thoroughly  slaked,  with  a  certain  proportion  of 
clay,  and  expose  the  mixture  to  calcination  in  a 
suitable  furnace.  The  resulting  product  is  called 
artificial  cement  "twice  kilned."  A  more  com- 
mon and  economical  method  is  to  substitute  for 
lime  some  soft  limestone,  like  chalk,  which  it  is 
easy  to  grind  and  form  into  a  paste.  A  great 
saving  is  thus  effected,  but  the  artificial  cement 
is  not  so  good  as  in  the  former  case,  as  the 
materials  are  not  so  thoroughly  amalgamated. 

The  analyses  of  various  hydraulic  limestones, 
contained  in  Chapter  VIII,  will  furnish  some  guide 
as  regards  the  proper  proportions  of  lime  and  clay 
to  be  mingled  together ;  but  to  determine  these 
more  accurately,  as  well  as  to  ascertain  the  time 
required  for  calcination,  recourse  should  be  had 
to  experiment  in  every  instance,  before  commen- 
cing operations  on  the  large  scale.  The  clay, 
having  been  selected  according  to  the  rules  given 
in  Articles  66-68,  should  be  mixed  with  fat  lime 
in  various  proportions ;  each  combination  may 
then  be  made  into  small  balls  about  one  inch  in 
diameter,  which,  after  being  allowed  to  dry  in 
the  air  for  a  brief  period,  should  be  left  in  the 
hottest  part  of  a  common  fire-place  during  several 
hours.     The  strength  of  the  products  thus  ob- 


ARTIFICIAL    CEMENT.  75 

tained  by  calcination,  may  be  ascertained  in  the 
same  manner  as  that  prescribed  for  testing  the 
qualities  of  natural  hydraulic  lime  or  cement. 

125.  Gen.  Paslev's  method  of  making  artificial  Manufac- 

11  r  ii  mu      tureinthe 

cement  in  the  large  way,  was  as  follows.  1  he  large  way. 
ingredients  employed  were  chalk,  ground  in  a 
mortar-mill  to  an  impalpable  powder  or  paste, 
and  blue  alluvial  clay  in  a  state  of  minute  divi- 
sion, obtained  usually  from  the  bottom  of  lakes, 
or  rivers  with  slow  currents.  When  this  species 
of  clay  is  not  to  be  procured,  pit  clay,  extremely 
fine  and  free  from  sand,  may  be  substituted.  In 
any  case,  the  clay  must  be  used  fresh,  for  if 
allowed  to  become  stale  by  exposure  to  the  air, 
its  qualities,  as  an  ingredient  of  artificial  cement, 
are  much  impaired. 

The  proportions  employed  were  137^  lbs.  of 
blue  clay  to  100  lbs.  of  pure  chalk,  perfectly  dry, 
nearly  equivalent,  by  measure,  to  a  cubic  foot  and 
a  half  of  clay,  for  every  cubic  foot  of  chalk  paste 
with  the  consistence  of  stiff  mortar.  It  was 
found  more  convenient  to  measure,  than  to 
weigh  the  ingredients,  and  two  boxes,  with  ca- 
pacities varying  as  one  and  a  half  to  one,  were 
employed  for  the  purpose  with  advantage.  The 
ingredients,  being  mingled  together  in  their 
proper  proportions,  were  thoroughly  worked,  in 
the  mortar-mill,  into  a  homogeneous  mass,  which 
was  then  made  into  balls  two  and  a  half  inches 
in  diameter,  and  allowed  to  dry  in  the  air,  under 
cover  from  the  rain,  some  forty-eight  hours.  The 
balls  were  finally  burned  in  the  same  kilns  as  those 
employed  for  calcining  natural  cement  stone,  one 
measure  of  coals  sufficing  for  eight  measures  of 
the  cement  balls. 

When  lime  is  employed  in  place  of  chalk,  the 
proportions,  recommended  in  general,  are  forty 


76  TREATISE    ON    MORTARS. 

pounds  of  quick  lime  to  one  hundred  pounds  of 
clay,  or  thirty-nine  pounds  of  the  former  to  a 
cubic  foot  of  the  latter.  The  lime  must  be 
thoroughly  slaked  into  paste,  before  admixture 
with  the  clay,  and  less  fuel  will  be  required  for 
the  calcination,  but  in  all  other  respects,  the  pro- 
cess is  similar  to  that  employed  with  chalk.* 

Hydraulic  limes,  of  any  required  degree  of 
energy,  may  be  fabricated  in  the  mode  just  de- 
scribed, by  varying  the  proportions  of  clay :  but 
as  these  limes  are  always  liable  to  injury  from 
exposure  to  the  air,  Gen.  Treussart  recommends 
that  the  clay  and  lime  be  calcined  separately,  and 
kept  unmixed  until  the  mortar  is  to  be  prepared. 
It  becomes  then  necessary  to  describe  the  mode 
of  manufacturing 


ARTIFICIAL    POUZZOLANAS. 

Manufac-  126.  The  experiments  necessary  for  determin- 
la'ge'way!  ing  a  choice  of  clays,  as  well  as  the  time  requisite 
for  their  calcination,  have  been  described  in  Arti- 
cles 66-68.  The  material  having  been  selected, 
is  kneaded  into  balls  the  size  of  the  fist,  or  small 
prisms,  by  means  of  a  mould,  and  may  then  be 
calcined  in  any  mode  that  admits  of  free  contact 
piate  ii.  with  the  air.  The  rectangular  lime-kiln,  Fig.  2, 
in  which  bricks  are  sometimes  burned  in  conjunc- 
tion with  lime,  usually  has  a  powerful  draught, 
and  is,  therefore,  well  adapted  for  the  purpose. 
The  conical  kilns  also  may  be  made  to  answer 
the  same  object,  by  a  slight  modification,  in  order 
to  increase  the  draught  of  air.  When  it  is  neces- 
sary to  construct  a  furnace  for  the  manufacture 

*  Pasley,  pp.  275,  283. 


ARTIFICIAL    POUZZOLANAS.  77 

of  artificial  pouzzolana,  that  represented  in 
Figs.  14,  15,  is  recommended  by  Gen.  Treussart,  Plate  iv. 
as  possessing  a  convenient  form.  The  hearth  is 
pierced  with  holes,  as  exhibited  in  the  plan,  and  a 
fire  of  wood  is  made  in  the  arches  below,  so  that 
the  clay  is  calcined  in  a  current  of  air.  If  the 
clay  to  be  used  is  greasy,  the  expense  of  temper- 
ing may  be  saved  ;  it  may  be  cut  at  once  from 
the  bank  in  pieces  of  the  form  and  dimensions  of  # 
common  bricks.  These  should  be  first  dried  in 
the  air,  and  then  placed  on  their  edges  upon  the 
hearth  of  the  furnace,  a  small  distance  asunder. 
Their  position  should  be  oblique  with  respect  to 
the  axis  of  the  kiln,  and  the  second  layer  should 
cross  the  first.  When  the  bricks  attain  the  proper 
color,  discovered  by  previous  experiment,  they 
are  removed  from  the  furnace.  They  may  now 
be  reduced  to  powder  in  the  same  manner  as  that 
employed  for  pulverizing  natural  hydraulic  ce- 
ment.* 

When  the  calcined  product  is  pulverized  with 
difficulty,  the  crude  clay  should  be  dried  in  the 
air,  and  being  reduced  to  powder,  may  then  be 
burned  in  a  reverberatory  furnace.  A  layer  of 
the  dry  powder,  from  six  to  eight  inches  thick, 
is  placed  upon  the  hearth,  which  is  inclined  at  as 
great  an  angle,  as  the  clay  dust  will  admit  of, 
without  sliding.  The  front  part  of  the  hearth 
may  be  horizontal,  in  order  to  receive  a  fire  of 
wood,  which  is  diminished  from  time  to  time 
that  the  clay  may  be  stirred  by  a  rake,  and  thus 
be  calcined  in  free  contact  with  the  air.  By 
means  of  the  above-described  furnace,  the  opera- 
tion of  pulverizing  the  calcined  clay  may  be 
avoided,  when  we  have  no  suitable  machinery 
for  the  purpose.f 

*  Smith's  Vicat,  p.  61.  t  Treussart,  pp.  94,  95. 

7  * 


78  TREATISE    ON    MORTARS. 


CHAPTER    VI. 

ON  THE  PREPARATION  AND  APPLICATION  OF 
VARIOUS  KINDS  OF  MORTARS. 

Mortars  127 '.  The  general  composition  of  mortars 
having  been  discussed  in  a  preceding  chapter, 
I  propose  now  to  describe  the  practical  methods 
employed  in  their  preparation,  exhibiting,  in 
detail,  the  processes  adopted  at  Fort  Warren, 
Boston  Harbor. 

The  mortars  to  be  considered  will  be  arranged, 
for  the  sake  of  convenience,  into  four  classes : 
1st.  Pointing  mortar ;  2d.  Stucco  mortar ;  3d. 
Mortar  for  masonry ;  and,  4th.  Mortar  for  con- 
crete ; — what  I  have  to  say,  however,  upon  the 
last  head,  being  reserved  for  the  next  chapter. 

Mortar         128.  The  ingredients  of  the  mortars  used  at 
Fortrwa£  Fort  Warren,  were  common  lime  from  the  vi 


ren. 


cinity  of  Thomaston,  Maine ;  Rosendale  hy- 
draulic cement,  manufactured  at  Kingston,  in 
the  State  of  New  York  ;  and  quartzose  sea  sand, 
obtained  usually  from  Provincetown,  Cape  Cod, 
and  sometimes  from  Newburyport,  Massachu- 
setts. These  materials  were  all  of  excellent 
quality  ;  the  lime  had  no  hydraulic  properties, 
but  was  quite  rich,  yielding  a  large  volume  of 
paste  ;  the  cement  energetic,  setting  in  eight 
minutes  after  immersion,  when  tested  in  the 
mode  before  prescribed  ;  and  the  sands  extreme- 
ly heavy,  with  angular  grains,  consisting  almost 
entirely  of  quartz. 

The  Thomaston  lime  was  usually  purchased 
for  about  seventy  cents  per  cask  of  240  lbs ;  the 


PREPARATION    OF    MORTARS.  79 

hydraulic  cement,  for  half  a  cent  per  pound ; 
and  the  sand,  for  fifty  cents  per  ton  of  2000  lbs. ; 
all  delivered  at  the  work. 

The  following  table  affords  a  means  of  com- 
parison, as  regards  the  size  of  the  grains,  between 
the  two  sands,  from  Provincetown  and  Newbury- 
port,  respectively.  They  were  each  passed 
through  sieves  of  various  degrees  of  fineness, 
and  the  results  are  recorded  below ;  the  first 
column  showing  the  kind  of  sieve,  or  the  num- 
ber of  openings  comprised  within  the  space  of 
one  linear  inch,  and  the  others,  the  proportions 
by  weight  of  each  sand  remaining  on  the  differ- 
ent sieves : — 

No.  of  Sieve.  Provincetown.  Newburyport. 

12 025 005 

15 025 003 

21 096 020 

24 156 020 

30 597 151 

32 014 007 

38 017 046 

39 017 041 

50 014 206 

60 006 227 

Not  retained  by  sieves,  .033 274 

1.000  1.000 

The  Newburyport  sand,  as  it  appears,  is  finer 
than  the  other,  and  was  on  that  account  pre- 
ferred for  brick  masonry ;  though  the  Province- 
town,  being  somewhat  purer  and  heavier,  was 
regarded  as  the  better  sand  for  most  purposes, 
and,  during  the  past  year,  has  been  used. exclu- 
sively, at  Fort  Warren.  I  will  suppose,  there- 
fore, that  this  latter  sand  was  always  employed. 
When  perfectly  dry,  and  made  dense  as  possible, 
it  weighs  106  lbs.  per  cubic  foot,  and  contains 
an  amount  of  void  spaces  equal  to  thirty-five 
per  cent,  of  its  volume. 


80  TREATISE    ON    MORTARS. 

veaaeifor  129.  A  prismatic  vessel,  with  projecting  handles 
mevo!d"ns  attached  to  the  sides,  having  a  base  of  one  square 
foot,  and  a  height  of  three  feet,  was  usually  em- 
ployed in  obtaining  interstices.  It  was  well 
soaked  for  at  least  twenty-four  hours,  and  the 
water  then  drained  out.  The  sand  was  first  de- 
prived of  its  moisture,  by  the  heat  of  an  oven, 
or  exposure  to  the  sun  for  several  days,  and  upon 
being  placed  in  the  prism  above-mentioned,  was 
as  much  compacted  as  possible,  by  ramming, 
striking  the  sides,  and  thumping  the  bottom  of 
the  vessel.  The  prism  being  filled  in  this  man- 
ner with  the  dry  sand,  water  was  then  slowly 
added,  until,  having  occupied  all  the  void  spaces, 
it  was  ready  to  overflow ;  and  the  quantity  used 
in  effecting  this  was  assumed  as  the  measure 
required. 

A  cylinder,  with  a  diameter  of  three  feet  and 
a  capacity  of  one  cubic  yard,  would  probably 
give  more  correct  results  than  the  vessel  above- 
mentioned  ;  though  the  voids  (.35)  of  the  Prov- 
incetown  sand,  determined  by  means  of  the 
prism,  vary  little  from  the  truth.  The  other 
method  of  measuring  interstices,  by  ascertaining 
the  difference  between  the  weight  of  a  cubic 
foot  of  quartz  and  that  of  a  cubic  foot  of  the 
sand,  condensed  as  much  as  possible,  gave  very 
nearly  the  same  proportion  of  voids,  viz.  34f  per 
cent. 

This  last  method,  described  in  Article  77, 
admits  of  very  general  application,  and,  I  am 
inclined  to  think,  may  always  be  employed  with 
advantage. 
Remarks.  130.  The  actual  quantities  of  the  ingredients, 
which  enter  into  the  composition  of  any  mortar, 
materially  depend  on  the  varying  conditions  of 
dampness  and  dryness,  looseness  and  compact- 


PREPARATION    OF    MORTARS.  81 

ness,  powder  and  paste,  in  which  they  may  be 
measured.  A  knowledge  of  the  following  average 
equivalents,  will,  therefore,  be  an  essential  pre- 
liminary to  the  full  understanding  of  the  propor- 
tions employed  at  Fort  Warren. 

One  cask  of  Thomaston  lime  weighs  240  lbs. 
net,  and  yields,  when  slaked,  eight  cubic  feet  of 
stiff  paste. 

One  cask  of  Rosendale  hydraulic  cement 
weighs  325  lbs.  net,  and  gives  three  cubic  feet 
and  three  quarters  of  stiff  paste. 

One  cubic  foot  of  Provincetown  sand,  damp 
as  it  usually  is  in  the  sand-bin,  and  measured 
loosely  after  the  ordinary  custom  of  laborers, 
weighs  eighty-six  pounds. 

One  cubic  foot  of  the  same  damp  sand,  com- 
pacted as  much  as  possible,  by  striking  the  sides 
and  thumping  the  bottom  of  the  vessel  contain- 
ing it,  weighs  ninety-eight  pounds. 

One  cubic  foot  of  Provincetown  sand,  perfectly 
dry,  but  measured  in  the  ordinary  loose  way, 
weighs  ninety-six  pounds. 

One  cubic  foot  of  the  same  dry  sand,  com- 
pacted as  much  as  possible,  in  the  manner  before- 
mentioned,  weighs  106  pounds. 

One  cubic  foot  of  the  same  dry  sand,  com- 
pacted as  much  as  possible,  and  then  brought  to 
the  same  state  of  dampness  in  which  it  is  usually 
found  in  the  sand-bin,  weighs  112  pounds. 

Putting  these  results  in  a  tabular  form,  we 
have  : 

1  cask  =  240  lbs.  of  lime  =*  8  cub.  ft.  of  stiff  paste. 
1  cask  =  325  lbs.  of  cement  =  3.75  cub.  ft.  of  stiff  paste. 
1  cub.  ft.  of  sand,  damp  and  loose,  =    86  lbs. 

1  cub.  ft.  of  damp  sand,  compacted,  =    98  lbs. 

1  cub.  ft.  of  sand,  dry  and  loose,  =    96  lbs. 

1  cub.  ft.  of  dry  sand,  compacted,  =  106  lbs. 

1  cub.  ft.  of  dry  sand,  compacted  and  made  damp  =  112  lbs. 


82  TREATISE    ON    MORTARS. 

This  last  weight  of  112  lbs.  per  cubic  foot  is 
supposed  to  represent  the  maximum  density  of 
damp  sand,  and  this  is  assumed  to  be  the  condi- 
tion of  the  sand,  in  fixing  the  proportions  of 
ingredients.  When  the  sand  is  measured  in 
other  conditions,  the  above  table  at  once  fur- 
nishes the  means  of  substituting  the  proper 
equivalents.  A  single  example  will  explain  what 
is  meant.  The  sand,  for  instance,  which  we 
intend  to  employ,  is  damp,  and  to  be  measured 
in  the  ordinary  loose  way.  The  mortar  is 
to  be  made  with  one  proportion  of  lime  paste 
and  two  proportions  of  sand,  or  say  four  cubic 
feet  of  lime  paste  and  eight  cubic  feet  of  sand. 
We  have  only  then  to  multiply  the  number  of 
cubic  feet  of  sand  by  112  and  divide  by  86,  and 
there  results  8  X  112  -^  86  =  10£  (nearly)  cubic 
feet  of  sand,  as  the  quantity  which  the  laborer 
should  be  directed  to  mingle  with  the  lime. 

A  box  of  convenient  size,  employed  for  meas- 
uring the  sand  at  Fort  Warren,  will  be  described 
hereafter ;  and  I  will  now  proceed  at  once  to  the 
consideration  of 


POINTING    MORTAR. 

Defined.  131.  Mortars  employed  in  masonry  usually 
contain  a  portion  of  fat  lime,  and  are  not  capable 
of  resisting  the  vicissitudes  of  the  weather  for 
any  great  length  of  time.  And,  indeed,  any  mor- 
tar used  in  the  construction  of  a  wall,  must  needs 
be  wanting  in  compactness  at  the  exterior  edge 
of  the  joints,  and  is,  therefore,  in  good  condition 
to  be  attacked  by  rain,  heat,  and  severe  frosts. 
Accordingly,  after  exposure  for  a  short  time,  it 
cracks  and  peels  off,  leaving  a  fresh  surface  to 


PREPARATION    OF    MORTARS.  83 

be  acted  upon  in  a  similar  way.  The  masonry 
is  thus  disfigured,  and  its  stability  endangered  in 
the  lapse  of  time.  It  becomes,  therefore,  neces- 
sary to  point  the  wall,  or,  in  other  words,  to  pro- 
tect its  joints,  by  filling  them  with  some  sub- 
stance which  will  withstand  all  the  injurious 
influences  before-mentioned. 

132.  Mortar,  to  be  well  adapted  to  this  object,  Requisites 
should  be  capable  of  attaining  great  hardness,  0mo°rtar.ng 
and  be  as  little  liable  to  crack  as  possible.    Such 

a  composition  may  be  made  by  mingling  hy- 
draulic cement  with  the  maximum  quantity  of 
sand,  and  the  minimum  quantity  of  water,  due 
regard  being  had,  at  the  same  time,  to  the  cohe- 
rence requisite  for  proper  manipulation. 

133.  The  above  ingredients,  hydraulic  cement,  ingredients 
sand  and  water,  constituted  the  mortar  used  for  empl°yed- 
pointing  at  Fort  Warren.     The  sand  (Province- 
town)  was  passed  through  a  sieve,  having  fifteen 
openings  to  the  linear  inch,  in  order  to  free  it 

from  any  pebbles,  or  coarse  grains  that  it  might 
contain,  and,  when  thus  screened,  weighed  102 
pounds  per  cubic  foot,  with  an  amount  of  void 
spaces  equal  to  thirty -six  per  cent. 

134.  The    cement    and    sand    were    always  Proportions 

.    i      j  ...  .     .  -  .  .      adopted  for 

weighed  with  a  view  of  ensuring  accuracy  in  pointing. 
their  proportions.  Those  adopted,  after  many 
experimental  trials,  were,  one  pound  of  cement 
powder  to  three  pounds  of  dry  sand,  or,  since 
a  cubic  foot  of  cement  paste  requires  eighty-six 
pounds  of  cement  powder,  and  a  cubic  foot  of 
the  screened  sand,  dry  and  thoroughly  compacted, 
weighs  102  pounds,  the  proportions  by  measure 
would  be  one  of  cement  paste  to  two  and  a  half 
of  dry  sand  at  its  maximum  density.  These  pro- 
portions, in  tabular  form,  are  : 

1  pound  of  cement  to  3  pounds  of  sand. 
1  measure  of  paste  to  2£  measures  of  sand. 


84  TREATISE    ON    MORTARS. 

They  gave  very  excellent  results  ;  the  voids  in 
the  sand  being  thirty-six  per  cent.,  the  quantity 
of  cement  was  nearly  the  minimum,  and,  pos- 
sibly, it  may  hereafter  be  reduced  with  advan- 
tage to  that  point,  when  the  masons  acquire  more 
experience  in  working  so  friable  a  composition. 
Mode  of       135.  The  mortar  was  prepared  by  an  intelli- 

theemortifr.  gent  laborer,  who  usually  weighed  out,  at  one 
time,  the  sand  and  cement  in  sufficient  quantities 
to  make  about  a  quart  measure  of  the  mixture. 
He  then  mingled  these  ingredients  together  in 
the  dry  state,  and  afterwards  placing  them  in 
an  iron  mortar,  and  adding  a  little  water,  he 
thoroughly  incorporated  them  by  pounding  with 
a  heavy  iron  pestle.  The  process  was  usually 
conducted  under  a  sail-cloth,  or  other  shelter,  to 
guard  against  the  drying  action  of  the  sun. 

The  mortar,  when  ready  for  use,  appeared  quite 
incoherent  to  the  eye,  only  sufficient  water  being 
added,  to  make  the  composition  adhere  together, 
if  pressed  strongly  between  the  fingers.  In  this 
state,  it  was  carried  to  the  masons,  in  small  por- 
tions, from  time  to  time  ;  the  laborer,  on  his  re- 
turn, continuing  to  beat  the  mixture,  until  all 
that  was  prepared  had  been  consumed,  when  a 
fresh  supply  of  the  composition  was  made  as 
before. 
Modeof       136.  Before    commencing    the    operation    of 

the6  join"!,  •pointing,  the  joints  of  the  wall  were  carefully 
cleaned  out,  the  old  mortar  being  removed  with 
a  suitable  instrument  to  a  depth  of  one  inch  at 
least.  It  is  most  convenient  to  do  this  during 
the  construction  of  the  masonry,  while  the  mor- 
tar used  for  laying  the  stone  is  still  soft.  The 
mason  himself,  or  the  laborer  who  attends  upon 
him,  immediately  after  each  course  is  laid,  may 
then  easily  rake  out  the  joints,  with  an  instru- 


PREPARATION    OF    MORTARS.  85 

ment  similar  to  that  shown  in  Fig.  1.     If  the   Plate  v. 
operation  is  delayed,  until  the  mortar  becomes 
hard,  it  may  then  require  the  use  of  a  hammer 
and  chisel,  at  considerable  increase  of  cost. 

It  sometimes  happened  that  the  stones  above 
and  below  a  joint,  almost  came  in  contact  ;  in 
such  a  case,  in  order  to  ensure  a  better  application 
of  the  composition,  and  preserve  some  degree  of 
uniformity  in  the  appearance  of  the  pointing,  a 
stone-cutter  was  employed  to  widen  the  joint  to 
about  one-eighth  of  an  inch.  The  hand  hammer 
and  chisel,  Figs.  2  and  3,  sufficed  for  this  pur-  Plate  v. 
pose. 

For  some  days  before  the  pointing  was  execu- 
ted, the  wall  was  made  thoroughly  wet,  in  order 
that  it  might  imbibe  as  much  water  as  possible. 
The  joints  too  were  well  brushed  out  and  moist- 
ened, a  short  while  before  the  application  of  the 
composition,  care  being  taken  to  remove  any 
superfluous  water.  The  mortar  then  became 
hard,  in  the  state  in  which  it  was  used,  without 
giving  up  any  of  its  moisture  to  the  wall,  or,  on 
the  other  hand,  receiving  from  it  any  additional 
quantity.  In  the  one  case,  its  energy  might  have 
been  impaired  by  too  rapid  desiccation,  in  the 
other  it  would  have  become  more  liable  to  crack 
in  drying.  It  is  very  important  that  the  masonry 
should  be  always  moist  during  the  application  of 
the  mortar,  and  the  better  to  ensure  this,  walls 
having  a  northern  exposure  should  be  pointed 
during  the  summer  season,  those  with  a  southern 
exposure,  during  the  spring  and  autumn.  When 
such  an  arrangement  is  impracticable,  the  mason- 
ry must  be  sheltered  from  the  sun  by  means  of  a 
sail-cloth,  or  some  temporary  contrivance. 

137.  The  implements  employed  by  the  mason    Mode  of 
in  applying  the  composition,  were  the  caulking  aPPllcat,on- 

S 


86  TREATISE    ON    MORTARS. 

riatev.  iron,  Fig.  4,  the  hammer,  Fig.  5,  the  jointer, 
Fig.  6,  the  ordinary  trowel,  and  a  straight  edge 
about  three  inches  wide,  and  six  feet  long. 

While  pointing,  two  masons  usually  worked 
with  the  same  straight  edge,  and  in  the  follow- 
ing manner.  The  joint  being  well  brushed  and 
slightly  damp,  though  exhibiting  no  moisture  to 
the  eye,  the  straight  edge  was  placed  beneath  it, 
and  supported  at  either  end  by  a  mason,  who, 
having  supplied  himself  with  a  small  portion  of 
the  material,  proceeds  to  fill  the  joint  as  well  as 
he  can,  by  striking  with  the  edge  of  the  trowel : 
he  then  employs  the  caulking-iron  and  hammer, 
and  by  repeated  blows  makes  the  mortar  per- 
fectly compact,  moisture  always  showing  itself 
on  the  surface  during  the  operation.  The  joint 
is  then  filled  a  second  time,  by  the  same  process 
as  before,  and  the  caulking-iron  again  used,  and 
this  operation  is  repeated,  until  the  mortar  thus 
forced  into  the  joint,  is  flush  with  the  surface  of 
piate  v.  the  wall.  The  jointer,  Fig.  6,  is  now  taken  in 
hand  by  the  mason,  who,  using  all  his  force, 
moves  it  backwards  and  forwards,  along  the 
length  of  the  joint,  until  he  succeeds  in  produc- 
ing a  polished  surface.  Sometimes  the  mason  is 
unable  to  give  smoothness  to  the  edges  of  the 
joints,  by  the  use  of  the  jointer  alone  ;  in  such 
a  case,  he  may  employ  the  trowel  also,  and  by 
pressing  it  firmly  against  the  edge  of  the  joint, 
and  giving  it.  the  same  motion  as  that  required 
with  the  former  instrument,  he  can  effect  the 
desired  result,  and  thus  complete  the  operation. 

The  thickness  of  the  jointer  should  be  regu- 
lated by  the  average  thickness  of  the  joint,  fitting 
it  pretty  nearly,  without  being  too  large. 

It  may  be  remarked,  generally,  with  reference 
to  the  instruments  used  for  pointing,  that  they 


PREPARATION    OF    MORTARS.  87 

were  such  as  the  smith's  shop  afforded  ;  and, 
though  answering  the  object  very  well,  they  are 
doubtless  susceptible  of  improvement. 

The  composition  and  process,  above  described, 
have  been  applied  only  to  regular  stone  masonry 
at  Fort  Warren,  but  with  little  modification  will 
answer  equally  well  for  brick-work.  In  rubble 
masonry,  with  irregular  courses,  it  may  be  neces- 
sary to  point  with  the  trowel  alone.  In  that  case, 
the  mortar  for  "  exterior  stucco  "  (Article  145), 
as  little  moist  as  may  consist  with  its  proper 
manipulation,  may  be  employed  with  advantage. 
It  should  be  applied  to  the  joints,  while  they  are 
still  moist,  soon  after  the  masonry  is  laid.  If  the 
pointing  be  deferred,  the  wall  should  be  made 
damp  ;  and  the  same  precautions,  as  in  regular 
masonry,  should  be  observed  with  regard  to 
scraping  out,  brushing  and  moistening  the  joints. 


STUCCO. 

138.  The  term  stucco,  though  formerly  applied  stuceo 
to  a  mixture  of  lime  and  powdered  marble  or 
plaster  of  Paris,  is  here  employed  in  a  much 
more  general  sense  ;  and  under  it  will  be  com- 
prised all  compositions  of  mortar,  intended  as 
coatings  for  ceilings  and  walls,  both  exterior  and 
interior. 

139.  Stucco  work,  thus  far  at  Fort  Warren,  Remarks, 
has  been  confined  to  the  exterior,  none  of  the 
quarters  having  yet  received  their  interior  finish. 
Nevertheless,  though  exterior  stucco  requires  most 

care,  and  is  by  far  the  most  important,  it  may  be 
well,  in  a  practical  paper  of  this  kind,  to  give 
some  brief  information  with  reference  to  the 
more  common  processes  of  interior  plastering. 


88  TREATISE    ON    MORTARS. 

implements      140.  The  only  implements  used  by  the  plas- 

used  in  .....  .,  J  , 

plastering,  terer,  which  it  consists  with  my  purpose  to  de- 
scribe, are,  the  plastering  or  laying-on  trowel,  the 
hawk,  and  the  float.  The  plastering-trowel  is  a 
thin  plate  of  hardened  iron  or  steel,  about  nine 
inches  long  and  three  inches  wide,  and  some- 
times rounded  at  one  end  ;  it  is  slightly  convex 
on  the  face,  and  to  the  back  is  attached  a  rounded 
wooden  handle,  by  which  the  workman  grasps  it. 
This  instrument  should  be  kept  perfectly  clean 
and  dry,  when  it  is  not  actually  in  use,  as  the 
slightest  rust  might  disfigure,  not  a  little,  any 
fine  work  upon  which  the  plasterer  is  employed. 
The  hawk  is  a  piece  of  board,  about  ten  inches 
square,  used  for  conveying  a  small  portion  of 
mortar  to  the  wall,  to  be  there  spread  by  the 
trowel.  It  is  held  by  means  of  a  wooden  handle, 
fixed  at  right  angles  to  its  plane.  The  float  is 
also  of  wood.  It  is  shaped  somewhat  like  a 
plastering  trowel,  and  is  used  to  rub  over  the 
finished  work,  with  the  view  of  producing  a 
hard,  smooth,  and  even  face.* 
Mortars  141.  The  mortars  used  by  the  plasterer  are 
pksteJr.  called  "coarse  stuff,''  "fine  stuff,"  "  guage  stuff," 
&c,  besides  a  variety  of  stuccoes  and  cements. 
Coarse  stuff  contains  ox  or  horse  hair,  in  addi- 
tion to  the  ordinary  ingredients  composing  the 
mortar  of  the  brick-layer.  The  hair  should  be 
free  from  grease  or  filth  of  any  kind,  and  as  long 
as  it  can  be  procured,  and  when  matted  together, 
should  be  well  switched  before  it  is  employed. 
It  is  intended  to  act  as  a  sort  of  bond  to  net  or 
tie  the  whole  mass  together.  If  the  mortar  is  to 
be  made  with  common  lime  and  sand,  they  may 
be  used  in  the  proportions  of  one  of  lime  paste 

*  Encyclopedia  Britannica,  Art.  Building. 


PREPARATION    OF    MORTARS.  89 

to  two  of  sand,  and  one  measure  of  hair  may  be 
added  for  every  six  measures  of  the  lime  paste. 

But  a  mortar  of  common  lime  does  not  harden 
for  a  long  time,  except  upon  the  outward  crust, 
and  even  for  plastering  on  the  interior  walls  of 
any  important  work,  it  is  advantageous  to  add  to 
the  mortar,  a  small  proportion  of  hydraulic  ce- 
ment, not  less  than  one  of  cement  paste  to  six  of 
lime  paste.  When  this  is  done,  we  may  further 
add  one  and  a  half  volumes  of  sand  for  each 
volume  of  cement  paste. 

Fine  stuff  is  the  putty  of  white  lime,  thorough- 
ly slaked  or  rather  macerated  in  water,  and  then 
dried  to  the  proper  consistence  for  working ;  it  is 
sometimes  mixed  with  a  small  quantity  of  hair. 

Guage  stuff  consists  of  three  parts  of  the  putty 
to  one  of  plaster  of  Paris,  and,  as  it  sets  rapidly, 
is  prepared  only  in  small  quantities  at  a  time. 

142.  When  the  plastering  is  to  be  applied  to  appi 
laths,  the   work  is  either   "  laid,"   or  "  pricked 
up,"  according  as  it  is  to  be  finished  with  one, 
two,  or  three  coats. 

"  Laying "  is  a  pretty  thick  coat  of  coarse 
stuff j  brought  to  a  tolerably  even  surface  with 
the  trowel  only.  For  this  purpose,  the  mortar 
must  be  well  tempered,  and  of  moderate  consist- 
ence, thin  or  moist  enough  to  pass  readily  between 
the  laths,  when  pressed  with  force,  and  bending 
over  them  so  as  to  form  keys ;  but  at  the  same 
time,  stiff  enough  to  allow  no  risk  of  its  falling 
apart  by  its  own  weight. 

If  the  work  is  to  be  in  two  coats,  "  laid  and 
set,"  the  laying  is  allowed  to  dry  a  little,  and  is 
then  rudely  swept  with  a  birch  broom,  to  roughen 
the  surface,  when  the  set,  a  thin  coat  of  fine  stuff, 
is  at  once  applied.  This  is  done  with  the  com- 
mon trowel  alone,  or  only  with  the  addition  of  a 
8* 


ica- 
tion. 


90  TREATISE     ON    MORTARS. 

hog's  bristle  brush,  which  the  workman  uses  in 
his  left  hand  to  rub  over  the  surface,  and  after- 
wards presses  and  smooths  it  with  the  trowel  in 
his  right.  Should  the  laid  work,  or  first  coat, 
have  become  very  dry,  it  must  be  slightly  moist- 
ened, by  sprinkling  or  throwing  water  upon  it 
from  a  brush,  before  the  set.  or  second  coat  is 
put  on,  otherwise  the  latter  may  shrink  in  drying, 
crack,  and  fall  away. 

In  floated  work,  or  work  with  three  coats,  the 
first  is  laid  roughly  on  the  laths,  the  object  being 
merely  to  make  the  keying  complete,  and  form 
a  surface  to  which  the  next  coat  may  attach  itself 
well.  It  should  be  of  pretty  equal  thickness 
throughout,  standing  about  a  quarter  or  three- 
eighths  of  an  inch  upon  the  surface  of  the  laths. 
When  it  is  finished,  and  the  mortar  yet  quite 
moist,  the  plasterer  scores  it  all  over  with  the 
end  of  a  lath,  in  parallel  lines  from  three  to  four 
inches  apart.  The  scorings  should  be  as  deep  as 
possible,  without  laying  bare  the  laths,  and  the 
rougher  the  edges,  the  better.  When  the  pricked 
up  coat  is  so  dry  as  not  to  yield  to  pressure  in 
any  degree,  preparations  are  made  for  the  float- 
ing. Ledges  of  wood,  or  margins  of  lime  and 
hair,  about  six  inches  wide,  called  screeds,  must 
be  made  at  the  angles  or  borders  of  the  surface, 
and  at  intervals  of  four  feet  apart,  throughout 
the  whole  area  to  be  floated.  These  screeds  are 
made  straight  with  each  other,  and  proved,  in 
every  way,  by  the  application  of  straight  edges. 
When  they  are  ready,  and  the  mortar  of  which 
they  are  composed  somewhat  hard,  the  inter- 
spaces are  filled  up  flush.  A  straight  edge  is  then 
made  to  traverse  the  screeds,  and  thus  bring  the 
whole  to  an  even  surface. 

When  the  floated,  or  second  coat,  is  sufficiently 


PREPARATION    OF    MORTARS.  91 

set  and  nearly  dry,  it  is  brushed  with  a  birch 
broom  as  before  described,  and  the  set,  or  hard 
finish,  then  applied.  When  the  surface  is  to  be 
colored  or  whitened,  the  third  coat  should  consist 
of  white  lime  putty  alone.  If  it  is  to  be  papered, 
a  small  quantity  of  hair  may  be  added  with  ad- 
vantage. When  the  surface  is  to  be  painted,  the 
mortar  should  be  composed  of  lime  putty  and 
fine  clean  sand,  in  the  proportion  of  two  measures 
of  the  former  to  one  of  the  latter. 

The  third  coat  should  be  worked  of  exactly 
the  same  thickness  throughout,  in  order  to  pre- 
serve the  advantage  gained  by  the  second  opera- 
tion. The  trowel  and  brush  are  considered  suffi- 
cient to  produce  good  work,  except  when  the 
walls  are  to  be  painted,  in  which  case  the  third 
coat  must  be  gone  over  with  the  hand-float.  In 
performing  this  operation,  the  surface  is  first 
made  as  smooth  as  possible  with  the  trowel,  for 
an  extent  of  two  or  three  yards.  The  workman 
then  takes  the  hand-float  in  his  right  hand,  and 
rubs  smartly  over  the  surface,  pressing  gently  to 
condense  the  mortar.  As  he  works  with  the 
float,  he  sprinkles  on  water  from  the  brush  in 
his  left  hand,  and  at  length  succeeds  in  giving 
the  wall  a  polish  like  that  of  marble. 

143.  The  operation  of  plastering  upon  brick  Plastering 
or  stone,  differs  only  in  name  from  that  described  bTicTwork! 
in  the  case  of  laths.  When  the  masonry  is  of 
recent  construction,  its  surface  should  be  well 
cleaned  from  dust,  and  slightly  moistened  before 
the  stucco  is  applied.  When  old  masonry  is  to 
be  plastered,  the  mortar  should  be  raked  from 
the  joints  to  the  depth  of  half  an  inch,  and  the 
surface  made  perfectly  clean  ;  if  blackened  by 
smoke,  or  at  all  greasy,  it  should  be  scraped  or 
roughened,  and  it  must  always  be  well  moist- 


92  TREATISE    ON    MORTARS. 

ened  with  water,  before  the  plastering  is  com- 
menced.* 


EXTERIOR    STUCCO. 

Means  of  144.  Ordinary  mortars,  or  mixtures  of  fat  lime 
stucco"  and  sand,  should  never  be  employed  for  stucco- 

fetiimL  ing  the  exterior  of  walls  ;  but  in  those  situations 
in  which  it  is  impossible  to  avoid  the  use  of  fat 
limes  for  the  above  purpose,  Capt.  Smith  recom- 
mends a  simple  means  of  improving  the  quality 
of  the  mortar,  which  has  been  long  practised  by 
the  natives  of  India.  It  consists  in  mixing  the 
lime  with  jaghery  water,  that  is  to  say,  with  a 
solution  of  coarse  sugar  or  molasses  ;  about  one 
pound  of  sugar  to  every  eight  gallons  of  water 
used  in  mixing  the  stucco,  will  be  sufficient,  ex- 
cept for  the  last,  or  floated  coat,  when  the  proper 
proportions  are  one  pound  of  sugar  for  every  two 
gallons  of  water.  The  influence  of  the  sugar 
upon  the  solidification  of  the  outer  crust  is  very 
marked,  and  stuccoes  prepared  with  jaghery  have 
been  known  to  resist  the  action  of  the  air  for  cen- 
turies, f 

stuccoat  145.  The  ingredients  of  the  stucco  used  at 
°rren  "  Fort  Warren,  were  hydraulic  cement  and  the 
sand  before  described.  The  proportions  adopted 
were  one  volume  of  stiff  cement  paste  and  one  and 
two-thirds  volumes  of  damp  sand  perfectly  com- 
pacted, or  what  amounts  to  the  same  thing,  one 
measure  of  cement  powder  and  two  measures  of 
sand  measured  loosely.  The  mortar  was  com- 
monly prepared  in  small  quantities  (half  a  cubic 
foot)  at  a  time,  in  order  that  it  might  be  all  used 


*  Encyclopedia  Britannica,  Art.  Building 
t  Smith's  Vicat,  p.  84. 


PREPARATION    OF    MORTARS.  93 

before  it  had  set,  and  it  was,  therefore,  most  con- 
venient to  measure  the  cement  in  the  state  of 
powder,  and  the  sand  in  the  ordinary  manner. 
The  ingredients,  in  the  proportions  above-men- 
tioned, were  intimately  blended  by  a  few  turns 
with  the  shovel,  sufficient  water  being  added  to 
produce  the  ordinary  consistence  of  mortar  de- 
signed for  plastering. 

146.  When  brick- work  was  to  be  stuccoed,  the  Mode  of 
joints  were  previously  raked  out  for  half  or  three-  tlllmhie. 
quarters  of  an  inch  in  depth  (an  operation  always 
performed  most  economically  during  the  con- 
struction of  the  masonry).  The  surface  of  the 
bricks  was  then  freed  from  any  dirt  or  dust  that 
might  have  gathered  upon  it,  and  thoroughly 
moistened,  or  rather  made  wet,  that  it  might  not, 

by  its  faculty  of  absorption,  deprive  the  stucco  of 
its  moisture  too  rapidly.  If  the  brick- work  be 
old,  or  covered  with  tar  or  grease  of  any  kind, 
its  surface  should  be  scraped  and  roughened  by 
scoring  it  with  a  light  axe,  before  the  plasterer 
begins  operations. 

147.  The  implements  which  he  requires,  are  Application 
the  plastering  trowel  and  hawk,  before  described. 

The  mortar  is  applied  in  a  single  coat,  not  ab- 
solutely laid  on  at  once,  but  great  care  is  taken 
that  the  outer  portion  should  be  added,  while  the 
first  is  still  soft,  so  that  the  two  should  form  one 
mass.  With  this  view,  the  first  is  made  some- 
what thinner  than  the  second,  in  order  that  the 
workmen,  in  applying  it,  may  by  the  exertion  of 
his  full  strength,  force  the  stucco  into  all  the 
joints  and  crevices  of  the  brick-Avork.  When 
two  or  more  square  feet  are  covered  with  a  thin 
coating  in  this  way,  and  while  the  mortar  is  yet 
quite  soft,  the  second  part  of  the  coat  is  laid  on, 


94 


TREATISE    ON    MORTARS. 


Remarks. 


Stuccoinj 
concrete. 


the  whole  (about  half  an  inch  thick)  being  well 
compressed  so  as  to  form  one  body. 

148.  Whenever  the  above  precautions  were 
carefully  observed,  the  results  were  always  satis- 
factory. If,  however,  the  first  part  of  the  coat 
is  allowed  to  set,  before  the  second  is  applied,  or 
if  any  portion  of  the  stucco  be  laid  on  loosely, 
after  the  ordinary  habit  of  masons,  it  will  be 
very  liable  to  become  loose  and  give  way,  when 
attacked  hy  rain  and  frost.  A  faithful  workman 
should  always  be  selected  for  the  operation,  but 
to  guard  against  any  inadvertence  on  his  part, 
the  whole  of  the  stuccoed  work,  after  it  has 
become  dry,  should  be  carefully  sounded  with  an 
iron  instrument,  in  order  to  discover  if  there  be 
any  defective  places.  These,  which  are  readily 
detected  by  their  hollow  sound,  should  then  be 
repaired  with  great  care,  the  precaution  being 
previously  observed  to  remove  the  old  mortar 
entirely,  and,  more  than  this,  to  roughen  and 
thoroughly  moisten  the  surface.  The  stucco 
must  not  be  allowed  to  dry  too  rapidly,  and,  with 
that  view,  should  be  well  protected  from  the  sun 
during  hot  weather,  for  some  days  after  the  ap- 
plication. 

149.  When  the  surface  to  be  plastered  is  one 
of  concrete,  the  mortar  should  be  laid  on,  while 
the  concrete  is  yet  moist,  and  if  any  part  has  been 
permitted  to  become  dry,  it  should  be  well  moist- 
ened with  water  before  the  application  of  the 
stucco.  The  mode  of  operation  in  plastering 
concrete  is  the  same  as  with  brick-work,  the 
great  requisite  and  difficulty,  in  every  case, 
being  to  induce  the  mason  to  bestow  labor  on 
the  process,  and  work  the  mortar  well  into  the 
substratum. 


PREPARATION  OF  MORTARS.  95 


MORTARS  FOR  STONE  AND  BRICK  WORK. 

150.  Intelligent  constructors  universally  agree  *e™d\nMj 
that  the  use  of  "ordinary  mortars,"  or  mixtures  mortar- 
of  fat  lime  and  sand,  should  be  proscribed  on  all 
important  works.  They  are  incapable  of  acquir- 
ing great  hardness,  and  of  resisting  the  inclemen- 
cies of  the  weather,  and  should  in  every  case, 
where  durability  is  desired,  be  improved  by  the 
addition  of  some  hydraulic  substance.  Never- 
theless, ordinary  mortars  are  in  general  use  among 

the  masons  of  the  country,  and  their  great  cheap- 
ness will  always  cause  them  to  be  employed  in 
the  erection  of  small  dwelling-houses  and  the 
like.  When  in  free  contact  with  the  atmosphere, 
but  shielded  at  the  same  time  from  the  action  of 
frost  and  rain,  they  may  in  time  become  hard, 
and  can  therefore  be  employed  without  great 
disadvantage  in  dry  situations  and  thin  walls. 

151.  In  ordinary  practice,  the  cohesion  of  the  oFin^edi- 
mortar  is  greatly  impaired  by  too  large  a  pi'op°i'-m0tSmoCrtaT 
tion  of  sand,  which  should  not  in  general  exceed 

two  volumes,  for  every  volume  of  lime  paste. 
The  equivalents  of  such  a  composition,  in  the 
form  most  convenient  for  small  operations,  would 
be, — one  cask  of  lime  =  240  lbs.  net.  =  8  cubic 
feet  of  stiff  paste,  and  sixteen  bushels  of  sand, 
damp,  and  measured  loose,  after  the  common 
custom  of  laborers. 

152.  It  was  supposed,  for  many  years,  that  the  L„nsedasb9 
longer  the  lime  was  slaked  before  it  was  used,    s?°,n  f 

,     °_  J      slaked. 

the  better  mortar  it  would  make.  Recent  expe- 
riments prove,  however,  that  this  is  not  the  case 
with  mixtures  of  fat  lime  and  sand  only.  Better 
results  are  obtained  with  such  mortars,  if  the 
paste  be   mixed  with  the   sand  as  soon  as  the 


96  TREATISE    ON    MORTARS. 

slaked  lime  has  become  cold,  and  care  should  be 
taken  to  use  no  more  water,  in  the  process  of 
extinction,  than  may  be  required  to  produce  a 
thick  pulp.*  The  reason  probably  for  this,  is 
derived  from  the  fact,  that  the  lime  does  not 
absorb  its  full  dose  of  water  in  being  converted 
into  paste,  but  continues  to  take  an  additional 
quantity,  until  the  saturating  limit  has  been  at- 
tained. The  process  of  absorption  goes  on  in 
the  mortar  by  an  internal  and  progressive  action, 
unaccompanied  by  any  change  except  an  altera- 
tion of  density,  and  by  consequence  of  hard- 
ness.! 
Mode  of  153.  In  preparing  ordinary  mortars,  it  will  be 
ordinary  convenient  to  place  the  unslaked  lime  upon  a 
mortars.  pian]{  floor,  under  shelter  from  the  sun  and  rain, 
and  then  (without  covering)  to  surround  it  with 
the  proper  quantity  of  sand.  The  water,  requisite 
to  produce  a  thick  paste,  previously  ascertained 
by  experiment,  should  be  poured  on  the  lime 
with  the  aid  of  watering  pots  of  known  capacity. 
The  lime  must  then  be  well  stirred,  so  as  to  ex- 
pose every  part  of  it  to  the  action  of  the  water, 
and  afterwards  left  to  itself,  until  the  vapors  have 
ceased  entirely.  The  ingredients  may  now  be 
thoroughly  incorporated  by  means  of  the  hoe  and 
shovel.  If  the  mixture  is  made  with  difficulty, 
a  little  water  may  be  added,  but  only  enough  to 
produce  a  homogeneous  mass, 
consist-  154.  The  consistency  of  the  mortar  thus  pre- 
Mtimated.  pared,  should  be  such  as  to  support,  without  very 
sensible  depression,  a  wire  with  a  diameter  of 
one-twelfth  of  an  inch,  and  loaded  to  weigh  one 
quarter  of  a  pound.  If  too  much  water  has  been 
inadvertently  added,  the  mortar  may  regain  its 

*  Totten's  Treussart,  pp.  134,  133— Vicat,  p.  39. 
t  Totten's  Treussart,  pp.  134,  138. 


PREPARATION    OF    MORTARS.  97 

virtues  which  have  been  lost  in  the  drowning,  by 
being  exposed  to  the  air,  and  stirred  from  time  to 
time  to  change  the  surface  of  contact.* 

155.  I  will  now  proceed  to  the  consideration  ImP,ements 

j,       .  \  -i  r\  „t  •  i        use"  ln  ma- 

oi  the  mortars  employed  at  t  ort  Warren,  m  the  kingmor- 
construction  of  masonry,  including  both  stone  "warren0." 
and  brick-work.  The  implements,  used  in  their 
preparation,  were  the  hoe  and  shovel,  a  box  for 
measuring  the  lime  or  cement  paste,  a  wheel- 
barrow box  for  measuring  the  sand,  and  the 
mortar-mill  with  its  appendages. 

The  implements  employed  in  the  transportation 
of  the  above  mortars,  were  the  mortar  boxes  and 
mortar  cart. 

The  hoe  and  shovel  vary  little  from  the  ordi- 
nary form,  and  are  shown  in  Figs.  5  and  6.  For  Plata  vi. 
measuring  the  paste  of  lime  or  cement,  a  box, 
two  feet  square  and  nine  inches  deep,  with  an 
interior  capacity  of  three  cubic  feet,  was  some- 
times employed  with  convenience.  It  was  sup- 
ported by  handles  attached  to  the  sides,  about 
six  feet  long  and  projecting  about  two  feet  at 
either  end. 

The  wheelbarrow  box,  used  for  measuring  the 
sand,  Fig.  4,  differs  from  an  ordinary  wheel-  Plate  vr. 
barrow,  only  in  the  substitution  of  a  box  with 
the  exact  capacity  of  three  and  a  half  cubic  feet, 
in  place  of  its  usual  body.  The  top  is  furnished 
with  a  rim  of  iron,  the  edge  of  which,  lying  in 
one  plane  throughout,  permits  the  laborer  to 
strike  the  sand  with  a  straight  edge,  and  thus 
enables  him  to  obtain  always  the  same  quantity. 

156.  Two  mills,  or  machines,  for  making  mor-  Mortar-miii 
tar,  have  been  employed  at  Fort  Warren.     One   warren. 
was  built  shortly  after  the  commencement  of  he 

*  Raucourt,  p.  85. 


98  TREATISE    ON    MORTARS. 

work,  and  has  been  in  use  ever  since,  but  being 
found  insufficient  to  supply  all  the  mortar  re- 
quired, another  was  constructed  a  year  or  two 
ago. 

The  first,  which  is  the  smaller  of  the  two,  and 
in  some  respects  the  most  convenient,  may  be 
described  briefly  as  follows :  It  consists  of  a  cir- 
cular trench,  built  of  masonry,  with  sloping  sides, 
riate  vl  as  represented  in  the  cross  section,  Fig.  2.  In 
the  trench  rests  a  heavy  wheel,  eight  feet  in 
diameter,  furnished  with  a  tire  half  an  inch  thick, 
and  twelve  inches  broad,  and  loaded  by  having 
its  interior  space  filled  with  sand.  At  the  centre 
of  motion,  is  a  drum,  or  circular  mass  of  masonry, 
four  feet  eight  inches  in  diameter,  in  which  is 
firmly  fixed  a  vertical  axis  about  eight  inches 
square.  With  this  axis  is  connected  the  horizon- 
tal shaft  (also  about  eight  inches  square),  which 
passes  through  the  centre  of  the  wheel,  and  to 
which  the  horse,  which  works  the  machine,  is 
attached. 

The  distance  from  the  centre  of  motion  to  the 
centre  of  the  wheel  or  trench  is  seven  feet  six 
inches,  and  the  radius  of  the  horse  path  is  twenty 
feet. 

The  machine  is  sometimes  provided  with 
scrapers,  for  cleaning  the  wheel  and  sides  of  the 
trench,  but  as  the  workmen  have  sufficient  time 
while  the  wheel  is  in  motion,  to  scrape  down  the 
mortar  with  their  shovels,  when  necessary,  the 
mill  at  Fort  Warren  has  not  been  furnished  with 
any  such  arrangement.  The  space  comprised 
between  the  drum  and  trench,  is  used  as  a  re- 
servoir for  the  slaked  lime.  It  is  sufficiently 
capacious  to  contain  the  paste,  which  sixteen 
casks  of  lime  will  afford,  and  is  conveniently 
divided,  by  means  of  movable  radial  partitions 


PREPARATION    OF    MORTARS.  99 

into  sixteen  equal  parts,  so  that  the  laborer,  who 
prepares  the  mortar,  is  relieved  of  the  necessity 
of  measuring  the  paste. 

The  mill  is  protected  from  the  weather  by  a 
cheap  roof. 

157.  The  other  mortar  mill,  which  was  before  Larger mor- 
mentioned  as  in  use  at  Fort  Warren,  resembles    tarmilu 
the  one  just  described  in  its  form  and  mode  of 
construction,  and  differs  from  it  only  in  its  di- 
mensions, which  are  much  increased.     The  re- 
servoir for  the  slaked  lime  is  large  enough  to  hold 

the  paste  which  eighty  casks  will  yield.  The 
distance  from  the  centre  of  motion  to  the  centre 
of  the  trench  is  twelve  feet  six  inches,  and  to  the 
centre  of  the  horse  path,  twenty-five  feet.  The 
wheel  has  the  same  diameter  in  either  case.  As 
this  mill,  however,  was  capable  of  producing  a 
much  greater  quantity  of  mortar  than  the  other, 
it  was  most  advantageous  to  use  it,  when  the 
operations  were  large. 

The  basin,  containing  the  slaked  lime,  not 
being  divided  into  compartments  of  convenient 
size,  it  was  necessary,  in  every  case,  to  measure 
the  paste.  This  was  done  sometimes  with  the 
box  mentioned  in  Article  155,  but  more  usually, 
by  filling  a  portion  of  the  trench,  the  capacity  of 
which  had  been  previously  calculated.  The 
consistence  of  the  paste  thus  measured  varying 
at  different  times,  the  proportion  of  lime  con- 
tained in  the  mortar  was  not  so  constant  as  when 
the  smaller  mill  was  used,  and  it  was,  therefore, 
most  desirable  to  employ  the  latter,  when  the 
consumption  of  mortar  was  not  very  great. 

158.  Each  mill  is  placed  in  the  vicinity  of  asiakingthe 
pump,  immediately  under  the   spout   of  which     hme' 
stands  the  box  L,  seven  feet  long,  five  feet  broad, 

one  foot  four  and  a  half  inches  deep,  used  for  sla- 


100  TREATISE  ON  MORTARS. 

king  the  lime.  This  box  is  connected,  at  one 
extremity,  with  a  small  compartment,  in  the 
bottom  of  which  is  an  iron  grating,  which  allows 
the  fluid  paste  to  pass  out  into  the  reservoir,  but 
retains  the  stones  and  imperfectly  slaked  lumps 
of  lime.  During  the  process  of  slaking,  the  com- 
partment is  separated  from  the  rest  of  the  box  by 
a  movable  board,  which  slides  in  grooves  made 
water  tight,  with  a  little  of  the  lime  putty. 

The  board  being  in  its  place,  water  is  pumped 
into  the  box  in  sufficient  quantity  to  convert  the 
lime  (three  casks  at  once)  into  a  thin  cream,  that 
will  readily  run  off  through  the  grating.  The 
lime  is  then  added  and  well  stirred,  in  order  to 
break  up  the  lumps,  a  large  hoe,  D,  being  usually 
employed  for  the  purpose.  When  the  slaking  is 
completed,  the  sliding  board  is  raised  and  the 
cream  conveyed,  by  means  of  the  trough,  JS,  at- 
tached to  the  grating  for  the  purpose,  to  the 
basin,  F,  where  it  is  allowed  to  remain  as  long 
as  possible  before  it  is  used. 
Remarks.  159.  The  lime,  thus  deluged  with  water,  loses 
probably  some  portion  of  its  binding  qualities; 
but  the  mortar  at  Fort  Warren  almost  always 
contains  hydraulic  cement ;  and  as  this  substance 
sets  rapidly,  it  is  highly  essential  that  the  lime 
should  be  thoroughly  slaked  before  the  admixture 
of  the  ingredients.  With  the  view,  therefore,  of 
ensuring  this,  as  well  as  from  regard  to  conveni- 
ence and  economy,  the  lime  is  reduced  to  the 
milky  consistence  before-mentioned,  and  allowed 
to  remain  in  the  vat  as  long  as  possible.  It  should 
be  remembered,  that  the  above  method  applies 
only  when  cement  is  added  to  the  lime.  When 
no  cement  is  used,  the  lime  must  be  slaked  in  the 
ordinary  way,  as  the  drenching  of  the  lime  would 
greatly  impair  its  binding  properties. 


PREPARATION  OF  MORTARS.  101 

It  is  convenient  to  fill  one  half  of  the  reservoir 
at  a  time,  in  order  that  the  slaking  of  one  part 
may  go  on,  if  need  be,  during  the  whole  time 
required  for  the  consumption  of  the  other. 

160.  The   proportions  of  the    ingredients   in  Proportions 
mortar  for  stone  masonry  at  Fort  Warren,  were  mortar  at 

r  it  Fort  War- 

aS  IOIIOWS:  rcn. 

1  cask  =  240  lbs.  net  of  Thorn,  lime  =8  cub.  ft.  stiff  paste. 

2  casks  =  650  lbs.  net  of  hyd.  cement  =  7£  cub.  ft.    "      " 
11  wheelbarrows  Prov.  sand  =  38£  cub.  ft.  damp  and  loose. 

or  reducing  the  sand  to  its  maximum  density,  the 
proportions  would  be, 

8  cubic  feet  of  lime  paste, 
7jL    tc       a    a  cement  paste. 

38.5  X  86  -7-1 12  =  29  cubic  feet  of  damp  sand, 
dense  as  possible,  producing  about  37  cubic  feet 
of  good  mortar. 

161.  In  brick  mortar,  which  it  is  desirable  to  Proportions 
have  somewhat  finer,  a  less  quantity  of  sand  was    mortal 
used,  and  the  proportions  adopted  were, 

1  cask  of  lime  =  8  cub.  feet  of  stiff  paste. 

2  casks  of  cement  =  7£  cub.  feet  stiff  paste. 

9  wheelbarrows  =31^  cub.  feet  sand,  damp  and  loose. 

Or  in  the  other  form, 

8  cubic  feet  of  lime  paste, 
7£   "        "     "  cement  paste, 

24  "        "     "  damp  sand  at  its  maximum  density,  producing 
about  32  cubic  feet  of  good  mortar. 

162.  The  above  were  the  ingredients  and  pro-  Remarks, 
portions  of  the  mortars  commonly  employed  at 

the  public  works,  in  Boston  Harbor.  In  construct- 
ing, however,  the  intrados  of  arches,  or  the  jambs 
of  openings,  with  pressed  bricks,  ordinary  mortar 
(fat  lime  and  sand)  was  generally  used  ;  as  hy- 
draulic cement  was  found  to  have  an  injurious 
action  on  the  face  of  brick-work. 
9* 


102  TREATISE  ON  MORTARS. 

The  simple  paste  of  hydraulic  cement  ought 
always  to  be  preferred  in  the  construction  of  tanks 
and  cisterns  for  holding  water ;  and  mixed  with 
a  small  proportion  of  fine  sand,  it  has  been  usually 
employed  at  Fort  Warren,  in  laying  very  "  fine 
hammered"  stone  masonry.  In  either  of  these 
cases,  however,  the  mortar  should  be  made  by 
hand,  in  small  quantities,  as  it  may  be  required. 
rfrtoneuui  1^3.  It  was  remarked  in  a  previous  chapter, 
brick-mor-  that  the  ingredients  of  mortar  are  more  thoroughly 
incorporated,  when  they  are  mixed  by  a  machine 
instead  of  being  worked  by  hand.  In  accordance 
with  this  view,  as  well  as  to  reduce  to  paste  any 
refractory  particles  of  lime,  one  of  the  mills 
before-mentioned,  was  always  employed  at  Fort 
Warren,  for  preparing  mortar  in  the  large  way. 
The  process  was  the  same  with  both  brick  and 
stone  mortar,  and  consists  essentially  as  follows : 
The  proper  quantity  of  lime  paste  is  first  placed 
in  the  trench  or  trough  of  the  mortar-mill.  (In 
the  case  of  the  smaller  mill,  no  measurement  is 
necessary  for  this  purpose,  as  the  laborer  merely 
empties  one  of  the  compartments  of  the  reservoir.) 
About  half  the  quantity  of  sand  intended  for  the 
batch  of  mortar,  is  now  put  with  the  lime,  in 
different  parts  of  the  trench.  It  is  removed  from 
Plate  vi.  the  sand  bin  by  means  of  the  wheelbarrow,  Fig.  4, 
which  is  used  for  measuring  the  sand,  the  laborer 
throwing  it  in  loosely  with  his  shovel,  and  care- 
fully striking,  each  time  the  vessel  was  filled. 
The  mill  is  then  set  in  motion,  and  the  above 
ingredients  are  thoroughly  incorporated  with  each 
other.  This  being  effected,  the  remainder  of  the 
sand  and  the  hydraulic  cement  (in  the  state  of 
powder)  are  then  added,  and  the  whole  worked 
into  a  homogeneous  mass,  sufficient  water  being 


PREPARATION  OF  MORTARS.  103 

supplied  from  the  trough  O,  Fig.  2,  to  produce  a 
mixture  somewhat  soft.* 

While  the  grinding  is  in  progress,  the  work- 
men should  carefully  scrape  down,  with  their 
shovels,  any  mortar  that  may  collect  upon  the 
wheel  and  sides  of  the  trench,  in  order  that  all 
the  materials  may  be  intimately  blended,  without 
any  loss.  The  mortar  when  properly  worked  by 
the  machine,  is  placed  in  boxes,  of  convenient 
size,  for  transportation  to  the  different  parts  of  the 
work. 

The  smaller  mill  will  make  about  600  cubic 
feet  of  mortar  in  a  day  of  ten  hours ;  the  larger 
mill  about  twice  that  quantity  in  the  same  time. 

164.  The  following  analyses  exhibit  the  cost    cost  of 

o  *  mortars  at 

of  the   mortars,  used  at  Fort  Warren,  for  stone  Ft.  wanen. 
and  brick  work,  respectively : 

Cost  per  cubic  yard  of  stone  mortar  prepared  by  machine. 
5.84  cub.  feet  of  lime  paste  =  0.73  casks  at  70  cts.  =  .51 

5.36    "       "     "  cement  paste  =  464.^  lbs.  at  £  ct.  =2.32 

20.98  "       "     «  sand  =  when  purchased  2853  lbs.  at  50 

cts.  per  ton,      .......       =  .71 

Laborer  making  mortar  0.38  day  of  10  hours  at  91  cts. 

per  day,  ........= .35 

Horses  making  mortar  0.09  day  of  10  hours  at  40  cts. 

per  day,  ........=  .04 

Stone  mortar  cost  per  cubic  yard,       .         .         .         .  =  $3.93 
"  "         "      "       «      foot  about  14.J  cts. 

Cost  per  cubic  yard  of  brick  mortar  prepared  by  machine. 

6.75  cubic  feet  of  lime  paste  =  84  casks  at  70  cts.  =    .58 

6.33  "  "  "cement"  =549  lbs.  at  £  cent,  =2.74 
20.25  "        "    "  sand  =  when  purchased  2754  lbs.  at 

50  cts.  per  ton, =    .69 

Making  per  cubic  yard  as  above,  laborers,  .         .         .  =    .35 

"          "      "       "       "      "       horses,     .         .         .  =    .04 

Brick  mortar  cost  per  cubic  yard,         .         .         .         .  =  $4.40 
"  "         "     «       «       foot  16J 

*  It  is  a  common  practice  with  some  officers  of  the  corps  of  en- 
gineers to  mix  the  cement  with  the  lime  before  any  sand  is  added ; 
and  it  is  thought  by  many  to  be  better  than  the  method  given 
above. 


104  TREATISE    ON    MORTARS. 

The  labor  was  the  average  of  a  season's  opera- 
tions ;  it  includes  the  slaking  of  the  lime,  but  not 
the  transportation  of  the  sand  from  the  vessel  to 
the  mill. 

^'uan"-3  165.  The  mortar  box,  used  in  transporting  the 
porting  mortar,  was  made  of  two  inch  plank,  and  pro- 
vided at  either  end  with  iron  hooks,  by  attaching 
to  which  the  chains  of  the  mortar  cart,  and  turn- 
ing a  crank  belonging  to  the  latter,  the  box  was 
held  suspended  underneath  the  cart.  The  mortar 
box  was  five  feet  six  inches  long,  three  feet  six 
inches  wide,  and  nine  inches  deep.     The  mortar 

plate  vu.  cart  and  box  are  shown  in  Figs.  1,  2  and  3. 

Remarks.  166.  When  in  small  operations,  mortar  is  made 
by  the  common  process,  the  same  order  of  pro- 
ceeding as  that  described  in  the  case  of  the  mill, 
should  be  followed.  Mortar  made  by  hand,  how- 
ever, is  much  more  costly  than  that  made  by  the 
machine,  and  always  inferior  in  quality  to  the 
latter,  for  it  is  the  interest  of  the  laborer  to  let 
the  wheel  move  as  long  as  possible,  the  time 
during  which  it  is  in  motion,  being  precisely  that 
in  which  he  has  the  best  opportunity  to  rest.* 

Quantity  of      167.  The  quantity  of  mortar  consumed  in  lay- 

nc'uWcryaPrdr  mg   a  cubic   yard   of  masonry,  must  obviously 

ofma80nry- depend  upon  the  size  and  character  of  the  mate- 
rials employed.  At  Fort  Warren,  where  the 
stones  are  massive,  a  cubic  yard  of  rubble  ma- 
sonry has  usually  required  about  four  cubic  feet 
of  mortar,  and  one-fourth  of  that  quantity  is 
usually  estimated  for  each  cubic  yard  of  ham- 
mered stone.  About  eight  cubic  feet  of  mortar 
are  consumed  in  building  a  cubic  yard  of  brick- 
work. 

Application      168.  In  constructing  masonry,  either  of  stone 

of  mortar. 

*  Totten  on  Mortars,  page  11. 


PREPARATION    OF    MORTARS.  10^ 

or  bricks,  care  should  always  be  taken,  before 
the  application  of  the  mortar,  that  the  materials 
to  be  cemented  should  be  well  brushed  and 
thoroughly  moistened.  Every  stone  should  be 
laid  in  a  good  bed  of  mortar,  and  be  well  settled 
in  its  place  by  heavy  blows  from  a  maul  or  mallet 
of  wood.  The  bricks  should  not  be  merely  laid, 
as  is  the  common  custom  of  workmen,  but  rubbed 
and  pressed  down,  so  as  to  force  the  mortar  into 
their  pores  and  crevices.  The  constructor  of 
every  work  should  direct  his  personal  attention 
to  the  vertical  joints  of  the  walls,  as  the  mason 
frequently  neglects  to  fill  them  with  mortar.  To 
obviate  the  ill  effects  of  his  carelessness  in  this 
regard,  some  builders  cause  the  several  courses 
of  masonry  to  be  grouted ;  that  is  to  say,  a  mor- 
tar made  liquid,  and  called  grout,  is  poured  on 
them  with  the  view  of  filling  all  the  joints  that 
have  been  left  vacant.  But,  at  best,  this  is  only 
doing  with  liquid  mortar,  what  may  be  done 
with  mortar  of  better  consistence  ;  and  grouting, 
being  objectionable  in  other  respects,  has  never 
been  employed  at  the  public  works  in  Boston 
Harbor. 


106  TREATISE  ON  MORTARS. 


CHAPTER    VII. 

ON  CONCRETE  AND  SOME  OF  ITS  APPLICATIONS. 

concrete  or      169.   The  French  beton  and  English  concrete 

beton  de-  -.    c  ■       •■  i  •    i. 

fined,  are  used  lor  similar  purposes,  and  are  essentially 
the  same.  The  mode  of  preparation  adopted  by 
English  engineers  differs  from  that  followed  by 
the  French  and  by  ourselves ;  but  the  resulting 
mass  in  both  cases  is  the  same,  or  differs  not 
more  than  mortars  differ  from  each  other,  and 
possesses  the  same  properties.  Beton  or  concrete 
is  nothing  more  than  a  mortar,  to  which  are 
added  coarser  materials  than  are  found  in  sand. 
The  term  concrete,  having  been  used  several 
years  by  the  English,  and  being  expressive  of 
the  composition,  is  generally  adopted  in  this 
country. 

Materials  170.  The  materials  proper  for  use  in  the 
making    manufacture  of  concrete,  are  hydraulic  lime  or 

concrete.  cementj  sand,  stone  broken  into  small  fragments, 
broken  bricks,  gravel,  shells,  and  the  like.  The 
coarser  ingredients  are  added  to  the  mortar  of 
sand  and  cementing  matter,  with  the  view  of 
giving  hardness  and  incompressibility,  and  of 
lessening  cost ;  and  this  cost  is  reduced  to  the 
utmost  by  the  use  of  fragments  of  various  sizes, 
and  sometimes  by  a  certain  proportion  of  gravel, 
in  order  to  make  the  sum  of  the  voids  as  small 
as  possible.  Gravel  is  often  used  alone,  in  place 
of  broken  stone  or  bricks ;  and,  at  some  of  the 
public  works  at  the  south,  the  shells  found  in 
great   abundance    on    the    sea-shore   have   been 


CONCRETE    AND    ITS    APPLICATIONS.  107 

employed  in  making  concrete  with  economy  and 
success. 

Wherever  operations  in  common  masonry  and 
concrete  are  carried  on  at  the  same  time,  every 
fragment  of  stone,  brick,  or  tile,  should  be  care- 
fully preserved,  as  it  can  always  be  employed 
with  advantage  in  the  manufacture  of  concrete. 
Of  the  materials  employed  at  Fort  Warren,  brick 
fragments  have  usually  been  preferred,  as  afford- 
ing the  best  results. 

17  L.  The  general  principles  contained  in  Chap-  Principles 

D  Mr  a  J:         1(1  deter- 

ter  III.  may  be  applied  in  determining  the  re-  mining  pro- 
spective quantities  of  the  ingredients  to  be  em-  port101 
ployed  in  making  concrete.  The  proportion  of 
cementing  matter  should  always  be  such  as  to 
form  good  mortar  with  the  sand  alone ;  and  the 
mortar,  thus  composed,  must  always  be  added  to 
the  solid  particles,  in  at  least  sufficient  quantity 
to  fill  up  their  voids.  This,  however,  would  be 
the  minimum  of  mortar,  and  would  rarely  pro- 
duce a  good  result.  An  excess  over  this  amount 
has  been  always  used  in  the  composition  of 
concrete  at  the  public  works  in  Boston  Harbor. 

172.  In   England,  concrete,   as  a  substratum,    English 
especially  in  dangerous  soils,  is  fast  superseding  preparing 
every  other  material  at  the  present  time  ;   and  concrete- 
I  will  first  proceed  to  give  a  short  account  of  the 
mode  in  which  it  is  prepared  in  that  country, 
before  describing  our  own  process,  to  which  my 
remarks  will  be  chiefly  directed. 

The  materials  usually  employed  in  the  manu- 
facture of  concrete  by  the  English,  are  hydraulic 
lime  (sometimes  common  stone  lime),  sand,  and 
some  other  material  like  coarse  gravel,  or  stone 
or  brick  fragments. 

The  lime,  fresh  from  the  kiln,  is  first  ground 
to  powder,  then  mingled  with  the  other  ingre- 


108  TREATISE  ON  MORTARS. 

dients  properly  proportioned,  and  the  whole 
well  blended  together  in  the  dry  state,  in  order 
that  the  slaking  of  the  lirne  may  be  delayed 
to  the  last  possible  moment.  When  the  mate- 
rials have  been  thoroughly  incorporated,  water 
is  added  in  sufficient  quantity  to  bring  the  mix- 
ture to  the  consistency  of  good  mortar,  and  the 
mass  again  turned  over  with  the  shovel  once  or 
twice,  with  all  practicable  expedition. 

The  concrete,  thus  prepared,  is  immediately 
transported  to  the  foundation,  and  thrown  into  it 
from  a  height,  when  it  can  be  done,  as  each 
shovelful  or  barrowful  compresses  the  mass  upon 
which  it  falls.  It  is  now  rapidly  spread,  levelled, 
and  sometimes  rammed,  by  laborers  placed  in 
the  trench  ;  after  which,  it  is  not  again  disturbed. 
In  setting,  it  swells  about  three-eighths  of  an 
inch  for  every  foot  in  height,  and  continues 
afterwards  to  expand  insensibly  for  a  month  or 
two.* 
Remark-son      173.  The  foundations  of  some  of  the  most 

concrete.    .  , 

important  structures  in  England  have  been  built 
entirely  of  this  kind  of  concrete,  and  eminent 
constructors  of  that  country  unite  in  giving  it 
an  excellent  character.  It  has  not,  however, 
been  used  to  any  extent  in  the  United  States, 
and  I  am  not  very  familiar  with  its  merits. 

In  general,  the  same  rules  apply  to  the  Eng- 
lish as  to  our  own  concrete,  which,  I  am  disposed 
to  think,  may  be  employed  in  constructions  with 
more  safety  and  advantage. 
Concrete.  ]  74.  Concrete  admits  of  a  great  variety  of 
applications.  Arches,  and,  indeed,  entire  build- 
ings, have  been  constructed  of  this  material 
alone  ;  and  it  furnishes  an  easy  and  cheap  means 

*  Smith's  Vicat,  p.  100. 


CONCRETE    AND    ITS    APPLICATIONS.  109 

of  forming  the  shafts  of  columns,  the  ornamental 
work  connected  therewith,  and  many  kinds  of 
artificial  stones.  Its  use,  however,  at  Fort  War- 
ren, has  been  confined  thus  far  to  the  founda- 
tions and  superstructure  of  walls,  and  the  roof- 
ings of  casemate  arches.  As  several  kinds  of 
concrete  were,  nevertheless,  employed  for  the 
above  purposes,  a  description  of  these  different 
compositions,  with  their  modes  of  preparation 
and  application,  will  perhaps  illustrate  the  sub- 
ject sufficiently  well,  without  the  necessity  of 
further  detail  upon  its  many  nicer  applications. 
I  will  accordingly  proceed  at  once  to  describe 
them  in  their  order,  first  taking  up,  under  each 
head,  those  mixtures  in  which  the  mortar  em- 
ployed was  composed  of  hydraulic  cement  and 
sand  only,  and  afterwards  those  in  which  fat 
lime  was  also  a  constituent  of  the  cementing 
matter. 


CONCRETE    FOR    FOUNDATIONS. 

175.  The   concrete   constituting    the  founda-  Sea-waii, 

I  O  V  6 1 1  fl 

tions  of  the  "sea-wall  at  Lovell's  Island"  was  isiami.* 
prepared  by  mingling  together  mortar,  composed 
of  hydraulic  cement  and  sand,  and  a  shingle 
or  gravel,  of  slaty  texture,  collected  from  the 
shores  of  the  island,  where  it  is  thrown  up  by 
the  sea  during  storms. 

This  gravel  consisted  of  pebbles  of  all  sizes, 
embracing  particles  of  the  bigness  of  a  pea, 
as  well  as  stones  some  six  inches  in  diameter ; 
and  the  different  sizes  were  so  well  proportioned 
as  to  give,  very  nearly,  a  minimum  amount  of 
void  spaces.     The  cement  and  sand  were  the 

*  Report  on  Construction  of  Sea-wall,  by  Col.  Thayer. 

10 


no 


TREATISE    ON    MORTARS. 


same  as  those  described  in  the  preceding  chap- 
ter. 
Mortar,        176.  A  batch  of  the  mortar  used  in  making 
po.^dCOa™d  the  beton  was  composed  as  follows : — 

piepared. 

Cement,  1  cask  =  3.75  cubic  feet  of  stiff  paste. 

Sand,  lO^  cubic  feet  damp  and  loose  =  8  cubic  feet  dense. 

It  was  made  by  hand  in  a  box  (7'  long,  5'  wide, 
11£"  deep)  that  was  found  to  be  of  convenient 
size,  though  constructed  for  another  purpose. 
One-half  of  the  sand  was  first  put  in  the  box 
and  spread  out,  then  a  cask  of  cement,  and  over 
this  was  spread  the  remainder  of  the  sand. 
Water  was  then  added  in  sufficient  quantity  to 
produce  a  somewhat  pliant  mixture,  and  the 
materials  mixed  together  in  the  usual  manner 
by  two  laborers,  assisted  occasionally  by  a  third. 
The  result  was  11  cubic  feet  of  mortar,  yielding 
as  when  used  to  make  the  concrete,  or  10|  cubic 
feet,  quite  stiff, 
cost  of        177.    1128   batches,    equal    to    428.22  cubic 

mortar.  -,  c   •,, 

yards,  cost  as  follows : — 

Cement,  362,400  lbs.,  at  half  a  cent  per  lb  ,       .     $1812  00 
Sand,  476.92  tons,  at  51  cents,  nearly,       .     .     .  243  24 

Labor,  including  the  transportation  to  the  plat- 
form, where  the  concrete  was  made,  the 
average  distance  being  40  yards,     ....  102  33 

Cost  of  428.22  cubic  yards  of  mortar,    .     .     .     $2157  57 

Analysis  of  cost  per  cubic  yard. 

Cement,  9.9  cubic  feet  of  paste  =  846  lbs.,       .     .     $4  23 
Sand,  22  cubic  feet  compacted  =  1.11  tons,      .     .  56 

Labor, 24 

Cost  of  mortar  per  cubic  yard, $5  03 

"      "         "         "       "      foot, 0  18| 


Composi- 
tion of  the 


178.  The  batch  of  mortar   above-mentioned 


CONCRETE    AND    ITS    APPLICATIONS.  Ill 

equal  to  10£  cubic  feet,  was  mixed  with  31^  cubic 
feet  of  gravel,  taken  from  the  depot  hard  by.  The 
void  spaces  of  this  gravel,  though  not  accurately 
ascertained,  were  estimated  by  Col.  Thayer  to  be 
between  twenty  and  twenty-five  per  cent.  The 
minimum  of  mortar  would  then  have  been  be- 
tween seven  and  eight  cubic  feet,  so  that  the 
concrete  contained  an  excess  of  mortar  of  more 
than  two  cubic  feet  per  batch,  to  compensate  for 
any  imperfection  in  the  manipulation. 

179.  The  concrete  was  prepared  by  first  spread-  Preparation 
ing  out  the  gravel  on  a  platform  of  rough  boards,  °  crete.  " 
in  a  layer  from  eight  to  twelve  inches  thick,  the 
smaller  pebbles  at  bottom  and  the  larger  on  the 
top,  and  afterwards  spreading  the  mortar  over  it 
as  uniformly  as  possible.  The  materials  were 
then  mixed  by  four  men,  two  with  shovels  and 
two  with  hoes,  the  former  facing  each  other,  and 
always  working  from  the  outside  of  the  heap  to 
the  centre,  then  stepping  back  and  recommencing 
in  the  same  way,  and  thus  continuing  the  opera- 
tion until  the  whole  mass  was  turned.  The  men 
with  hoes  worked,  each,  in  conjunction  with  a 
shoveller,  and  were  required  to  rub  well  into  the 
mortar  each  shovel  full,  as  it  was  turned  and 
spread,  or  rather  scattered  on  the  platform  by  a 
jerking  motion.  The  heap  was  turned  over  a 
second  time  in  the  same  manner,  but  in  the  oppo- 
site direction,  and  the  ingredients  were  thus 
thoroughly  incorporated,  the  surface  of  every 
pebble  being  well  covered  with  mortar.  Two 
turnings  usually  sufficed  to  make  the  mixture 
complete,  and  the  resulting  mass  of  concrete 
(33£  cubic  feet)  was  then  ready  for  transportation 
to  the  foundation. 

The  success  of  the  operation,  however,  depends 
entirely  upon  the  proper  management  of  the  hoe 


112  TREATISE    ON    MORTARS. 

and  shovel,  and  though  this  may  be  easily  learned 
by  the  laborer,  yet  he  seldom  acquires  it  without 
the  particular  attention  of  the  overseer. 
Force  era-  180.  The  ordinary  force  at  work,  exclusive  of 
ployed.  fliQ  mortar  makers,  was  as  follows : — four  men 
bringing  gravel  and  mixing  ;  two  men  transport- 
ing concrete  to  trench  (each  filling  his  barrow) 
and  aiding  to  bring  gravel ;  one  man  at  trench, 
levelling  and  ramming;  in  all  seven  men,  to 
which  were  occasionally  added  two  others,  in 
which  case  four  men  were  kept  constantly  em- 
ployed with  the  hoe  and  shovel,  turning  and 
mixing. — The  mean  distance,  over  which  the 
concrete  was  transported,  was  twenty-two  yards, 
and  the  paths  nearly  horizontal. 
Application  181.  The  concrete  was  transported  to  the 
crete.  trench  in  wheelbarrows,  and  there  levelled  and 
well  rammed  by  a  single  laborer,  in  layers  about 
a  foot  thick,  the  foundation  being  brought,  how- 
ever, to  its  full  height,  before  the  lower  layers 
were  allowed  to  become  dry.  The  instrument 
used  for  ramming  was  a  cylinder  of  wood,  about 
eight  inches  in  diameter  and  eight  inches  high, 
with  its  base  faced  with  thick  sheet  iron,  and 
furnished  with  a  handle,  between  three  and  four 
feet  long.  The  foundation  varied  in  thickness 
from  one  foot  and  three-quarters  to  three  feet. 

Sometimes,  when  the  concrete  is  too  moist, 
the  mass  will  appear  to  shake  under  the  blows  of 
the  rammer,  after  the  manner  of  a  quagmire  ;  in 
such  a  case,  the  ramming  should  be  omitted,  and 
the  beton  merely  levelled  and  smoothed  off  with 
the  shovel.* 

The  best  consistence  is  that  which  allows  the 
mass  to  be  compressed  into  a  perfectly  compact 

*  Col.  Thayer's  Report,  Sea- Wall,  Lovell's  Island. 


CONCRETE    AND    ITS    APPLICATIONS. 


113 


body,  without  acting  as  above-mentioned,  and  at 
the  same  time  to  exhibit,  under  the  blows  of  the 
rammer,  a  little  free  water  upon  its  surface. 

But  all  our  experience  with  concrete,  generally, 
goes  to  show,  that  it  is  better  to  have  it  too  moist 
than  too  dry,  as  it  may  lose  all  its  strength  by 
too  rapid  desiccation ;  and  it  is  especially  neces- 
sary to  guard  against  this  latter  defect,  in  concrete 
made  with  mortar  containing  a  large  proportion 
of  hydraulic  cement,  as  this  substance  solidifies 
water  with  great  facility. 

182.  In  the  foundations  of  the  sea-wall,  there  Co3t  oftl,e 
were  in  all  431  batches,  producing  540.5  cubic 
yards,  measured  in  the  work,  the  cost  of  which, 
including  materials,  labor  and  contingencies,  is 
exhibited  in  the  followinsr  table  : — 


Concrete  for  foundations,  540.5  yards 
C  Cement,  138572  lbs.      .     .     . 
Materials.  <  Sand,  132.22  tons,    .... 
(  Gravel,  503.00  yards,    .     . 
f  Making  mortar,  35.00  days, 
Labor  }  Making  concrete,  58.90  days,      .     . 
"  |  Transporting  concrete,  29.45  days, 
[Ramming  concrete,  &c.  16.90  days, 
f  Tools,  implements,  ") 

Contingen- J  Platforms,  runs,  I 

cies.        "j  Removing  sand  and  cement,  [ 
[Other  contingencies, 


$692  86 
92  72 
129  5S 
41  42 
67  84 
34  38 
21  53 

60  61 


Entire  cost, $1140  94 

Analysis  of  cost  per  cubic  yard,  foundation  concrete. 

mortar,      C  Cement,  256.37  lbs.  =  3  cub.  ft.   paste,       $1  28 

.17  cub.  ft.  I  Sand,  674  lbs.  ==6£  cub.  ft.  dense,  .     .     .  17 

Gravel,  25.13  cub.  feet, 24 

Making  mortar,  =  0.064  ~] 

Making  concrete,  =  0.109  '  _n  Qfi  ,  „ 

Transporting  concrete,     =  0.054  f —U,4°  aays'  *     "  6l 

Packing  concrete,  =  0.031  J 

Tools,  implements,  &c 11 


Concrete  for  foundation,  cost  per  cubic  yard, 

10* 


$2  11 


114  TREATISE    ON    MORTARS. 

scarp  wan  183.  The  foundation  courses  of  part  of  the 
°ren.  "  scarp  wall  at  Fort  Warren  rested  upon  a  substra- 
tum of  concrete  about  one  foot  thick.  The 
mortar,  like  that  used  at  Lovell's  Island,  was 
composed  of  cement  and  sand  only,  though  it 
was  much  richer,  the  proportions  being  as 
follows : 

Cement,  900  lbs.  =  10^  cub.  feet  stiff  paste, 

Sand,  21  cub.  feet  damp  and  loose  =  1G  feet  compacted. 

The  result  of  the  mixture  was  about  twenty- 
two  cubic  feet  of  mortar,  to  which  was  added  a 
due  proportion  of  gravel ;  and  the  concrete  was 
then  prepared  and  applied,  as  described  in  the 
case  of  the  sea-wall. 


FOUNDATION    CONCRETE    CONTAINING    FAT    LIME. 

Pintle  184.  In  laying  the  pintle  blocks  of  the  Barbette 
blocks.  gUns  on  tne  coverface,  where  the  ground,  being 
elevated,  is  much  more  dry,  a  portion  of  fat  lime 
was  used  as  an  ingredient  of  the  mortar,  for  the 
concrete  of  the  foundations.  Its  proportions  were 
as  follows  : — 

Lime,  1  cask  =  8  cub.  feet  of  stiff  paste, 

Cement,  975  lbs.  =  11.25  cub.  feet  of  stiff  paste, 

Sand,  42  cub.  feet  damp  and  loose  =  32  cub.  feet  dense. 

These  ingredients  were  mixed  together  in  the 
mortar-mill,  after  the  usual  manner,  and  produced 
forty-two  cubic  feet  of  yielding,  or  forty  cubic 
feet  of  stiff  mortar.  A  third  part  of  this  batch  of 
mortar,  say  thirteen  and  two-thirds  cubic  feet, 
was  employed  in  making  a  batch  of  concrete. 
It  was  mixed  for  this  purpose  with  22.50  cubic 
feet  of  granite  fragments  and  11.25  cubic  feet  of 
beach  gravel,  in  all  33.75  cubic  feet  of  the  small 
stony   materials,    which   measured,   after    being 


CONCRETE    AND    ITS    APPLICATIONS.  115 

mingled  together,  about  32.75  cubic  feet,  and 
contained  an  amount  of  voids  equal  to  thirty-five 
per  cent.  The  mode  of  preparing  the  concrete 
was  to  mix  the  gravel,  in  the  first  place,  with  a 
portion  of  the  mortar,  and  when  these  were  well 
incorporated,  to  spread  out  the  mass,  over  which 
were  then  spread,  first,  the  granite  fragments,  and 
afterwards,  the  remainder  of  the  mortar.*  The 
whole  was  then  worked  into  a  hpmogeneous  com- 
position, and  the  resulting  product  Was  thirty- 
eight  and  a  half  cubic  feet  of  concrete.  The 
average  size  of  the  granite  fragments  was  some- 
what less  than  that  of  a  hen's  egg,  and  the 
amount  of  their  void  spaces  about  forty-four  per 
cent.  The  gravel  was  not  sufficiently  fine  to  be 
well  adapted  for  filling  the  interstices  of  the 
coarser  fragments  of  granite.  Though  consist- 
ing, for  the  most  part,  of  small  pebbles,  it  con- 
tained them  of  all  sizes,  from  the  bigness  of  a  pea 
to  that  of  the  broken  stone.  In  texture,  it  was  a 
granitic  amygdaloid,  weighing  about  one  hundred 
and  sixteen  lbs.  to  the  cubic  foot,  with  void  spaces 
equal  to  thirty  per  cent. 

The  stone  fragments  were  obtained  by  break- 
ing up  the  waste  pieces  of  granite,  that  are  pro- 
duced in  the  common  operations  of  masonry. 
They  are  now  prepared  on  the  work  at  the  rate 
of  seventy  cents  per  cubic  yard.  The  gravel  was 
procured  from  the  sea-beach  in  the  vicinity  of 
Cohasset,  and  delivered  at  the  work,  for  fifty 
cents  per  ton  of  two  thousand  pounds. 

A  gravel  of  inferior  quality  is  sometimes  thrown 
up  during  storms  on  George's  Island,  where  Fort 
Warren  is  located,  and  when  collected  thence 
costs  but  little  more  than  one-third  of  that  sum. 

*  Some  constructors  prefer  mixing  all  the  mortar  with  the  gravel 
in  the  first  instance,  and  afterwards  adding  the  coarser  particles. 


116  TREATISE     ON    MORTARS. 

Had  this  cheaper  material  been  alone  employed, 
the  concrete  would  have  been  much  reduced  in 
price. 

The  following  analysis  exhibits  the  cost  of  a 
cubic  yard : — 

f  Lime— cask,  .23  at  70  cts $0  16 

|  Cement— lbs.  227  at  £  cent,      ....  1   13£ 

Materials.^  Sand  — ton,  .50  at  50  cts 25 

|  Granite — yard.  .58  at  70  cts 41 

(^  Gravel  — ton,  .45  at  50  cts 22£ 

j    ,             C  Making  mortar  in  mill,  .35  yd.  at  39  cts.  13£ 

I  Making,  carrying  and  packing  concrete,  30| 

Cost  per  cubic  yard  concrete, $2  62£ 

185.  As  the  "  breast  height  wall  "  was  a  struc- 
Breast    ime   0f  }ess    important    character,   the   concrete 

height  r  J 

waii.  foundation  upon  which  it  rested,  was  not  so  rich 
in  cement,  as  that  described  in  the  case  of  the 
"  pintle  blocks ;  "  the  proportion  of  lime  in  the 
mortar  being  one  cask  for  every  two  of  hydraulic 
cement. 


CONCRETE  IN  THE  SUPERSTRUCTION  OF  WALLS. 

186.  The  sea-wall  at  Lovell's  Island  (between 
construe-  the   foundations    and  capping)  was  faced   with 
tl0wa°[.*ea  blocks  of  granite,  laid  in  regular  courses  of  al- 
ternate   headers    and    stretchers,    two    feet    in 
"rise." 

As  soon  as  each  course  of  facing  stones  w^as 
laid,  the  wall  throughout  its  entire  thickness  (an 
average  of  six  feet)  was  levelled  off  with  concrete 
rammed  into  a  compact  body.  In  order  to  ensure 
perfect  adhesion  between  the  stones  and  concrete, 
the  surface  of  contact  was  first  well  brushed,  to 
free  it  from  dust,  then  moistened  with  water,  and 
coated  completely  with  mortar,  before  the  con- 
crete was  put  in  place. 

*  Col.  Thayer's  Report,  Sea-Wall,  Lovell's  Island. 


CONCRETE    AND    ITS    APPLICATIONS.  117 

During  the  operation  of  ramming,  the  concrete 
was  supported  in  rear  by  a  movable  boxing,  con- 
sisting of  a  couple  of  two-inch  planks,  about 
twenty  feet  long,  fastened  together,  end  to  end, 
with  battens,  and  supported  firmly  in  position  by 
braces  of  plank  or  joist.  This  boxing  could  be 
removed  with  safety  in  a  few  hours  after  the  con- 
crete was  "packed." 

187.  The  mortar  was  the  same  in  all  respects,    Mortar 
as  that  used  for  the   foundations  of  the   wall,  concrete. 
(See  Article  176.)     About  six  per  cent,  of  each 
batch  (10£  cubic  feet)  was  generally   used  for 
plastering,  as  above-mentioned,  and  the  remain- 
der,  9f  cubic  feet  of  mortar  was  mixed  with 

27]  cubic  feet  of  gravel,  collected  from  the 
beach  of  the  island.  The  ingredients  were  then 
thoroughly  incorporated  and  transported  to  the 
place  of  deposit,  in  the  manner  already  detailed. 

188.  The  force  commonly  employed  was  as  Force  em- 
follows  :- 

Two  men  bringing  gravel  and  mixing  ingredients,    .     .     2 
Two  men  transporting  concrete  and  mixing,  (two-fifths 

of  the  time  mixing), 2 

Two  men  at  the  wall,  one  plastering,  the  other  level- 
ling and  ramming, 2 

In  all, 6 

189.  There    were    consumed  in  backing  the  cost  of  the 
wall,  697  batches  of  concrete,  producing  795.7 
cubic  yards,  the  cost  of  which  per  cubic  yard  is 
shown  in  the  subjoined  analysis  : — 

9  cub.  ft.  C  Cement,  231  \  lbs.  =  3.28  cub.  ft.  paste,     $1  41 
mortar.   \  Sand,  741  lbs.  =  7.2  cub.  ft.  dense,     .        0  19 

Gravel,  24.1  cub.  ft., 0  23 

Making  mortar,  =  0.06"j 

Making  concrete,  =  J.02  I   =  Q^  .  Q  ^ 

Transporting  concrete,  =  U.Ub  j  J 

Packing  concrete,  =  0.06  j 

Tools,  implements,  &c Oil 

$2  31 


concrete. 


118  TREATISE  ON  MORTARS. 

Breast-  190.  The  construction  of  the  breast-height 
1  'wall  at  Fort  Warren  was  similar  to  that  of  the 
sea-wall  at  Lovell's  Island.  It  had  merely  a 
facing  of  hammered  stone,  backed  in  rear  with 
concrete,  which  was  supported  during  the  opera- 
tion of  ramming,  by  a  rough  boxing,  and  after- 
wards plastered  with  a  good  coat  of  cement 
stucco.  The  mortar  used  in  making  the  beton, 
was  the  same  as  that  employed  for  stone  masonry 
(see  Art.  160),  and  the  concrete  was  similarly 
composed  with  that  applied  to  the  roofing  of 
casemate  arches,  to  be  hereafter  described  (Art. 
194). 

piers  and       191.   The  scarp  wall  and  piers,  generally,  of 

wanen.  Fort  Warren,  are  constructed  with  large  blocks 
of  granite,  the  interspaces  of  which,  instead  of 
being  closed  up  in  the  usual  costly  way  by  small 
fragments  of  stone,  laid  in  mortar  by  a  mason, 
are  filled  with  concrete,  rammed  into  a  compact 
mass  by  a  common  laborer.  The  rammers  which 
he  employs  for  the  purpose,  are  usually  provided 
with  handles  some  three  feet  long,  and  have 
dimensions  varying  according  to  circumstances. 
They  are  cylindrical  or  cubical  in  form,  and 
made  either  of  wood  or  iron,  the  larger  spaces 
requiring  the  use  of  wooden  rammers,  the  smaller 

Plate  vi.  those  of  iron.  The  rammers  are  shown  in  Fig.  7. 
The  concrete  employed  was  the  same  as  the  com- 
mon roofing  concrete,  described  in  Art.  194. 

In  every  such  application,  the  precaution  should 
be  observed  to  moisten  the  surface  of  contact, 
and  smear  it  well  with  mortar,  before  the  con- 
crete is  put  in  place. 


CONCRETE   FOR  THE   ROOFINGS   OF   ARCHES. 

Two  kinds       192.  The  arches  of  the  work,  whether  of  brick 

used  at  1  ort  »  . 

AVarren.   0r  stone,  are  covered  or  rooted  with  concrete, 


CONCRETE    AND    ITS    APPLICATIONS.  119 

which  furnishes  an  easy  means  of  forming  the 
slopes  requisite  for  carrying  off  rain  water. 

Two  kinds  of  concrete  were  used  for  this  pur- 
pose ;  one  intended  for  the  outer  coating  of  the 
roof,  not  exceeding  six  inches  in  thickness,  in 
which  the  mortar  employed  consisted  of  sand  and 
cement  only  ;  the  other  constituting  the  mass  of 
the  roof,  made  with  the  same  mortar  as  that  com- 
monly used  in  stone  masonry  and  prepared  by 
the  machine. 

193.  For  the  outer  coat  of  concrete,  the  pro-    J^'"1 
portions  of  the  mortar  were  : —  concrete. 

Cement,  450  lbs.  =  5.25  cub.  ft.  stiff  paste, 

Sand,  10£  cub.  ft.  damp  and  loose  =  8  cub.  ft.  dense, 

and  the  result  of  the  mixture  was  eleven  cubic 
feet  of  mortar.  This  batch  was  mixed  with 
22.5  cubic  feet  of  brick  fragments,  and  some- 
times a  mixture  of  brick  and  gravel  in  equal 
proportions,  and  produced  nearly  one  cubic  yard 
of  concrete.  The  ingredients  were  incorporated 
in  the  usual  manner,  the  precaution  being  ob- 
served to  soak  the  bricks  thoroughly,  and  for 
some  time  before  they  are  mixed  with  the  mor- 
tar, in  order  that  they  may  imbibe  as  much  water 
as  possible. 

194.  In   preparing   the   common  roofing  con-  common 

i    •     i         /•  i  i  c  c  roofing 

crete,  one-third  of  a  batch  01  mortar  tor  stone  concrete, 
masonry,  (Art.  160),  =  12.33  cubic  feet,  was 
mixed  with  18.75  cubic  feet  of  granite  fragments, 
and  11.25  cubic  feet  of  gravel,  making  together 
30  cubic  feet,  or  after  union  about  28|  cubic  feet 
of  solid  materials,  with  an  amount  of  void  spaces 
equal  to  34!  Per-  cent.  The  resulting  product 
was  32|  cubic  feet  of  concrete. 

195.  The  cost  per  cubic  yard  of  the  concrete    coatof 
used  for  the  outer  coat,  as  well  as  of  that  form- 


120  TREATISE  ON  MORTARS. 

ing  the  mass  of  the  roof,  is  exhibited  in  the  sub- 
joined analyses  : — 

M         C  Cement,  450  lbs.  at  \  ct.  per  lb $2  25 

.   |  '  <  Sand,  (including  waste)  =  .54  ton  at  50  cts.  27 

na       (  Broken  bricks,  22£  cub.  ft.  ==  .83  yd.  at  35  cts.  29 

I    ,        C  Making  mortar,  .41  cub.  yd.  at  39  cts.    ...  ]6 

'  (  Making,  transporting  and  packing  concrete,  &c.         59 

Cost  per  cubic  yard, $3  56 

Analysis  of  cost  per  cubic  yard  of  common  roofing  concrete. 

f  Lime,  .28  cask,  at  70  cts $0  19 

M  |  Cement,  180  lbs.  at  £  ct 90 

■   i  '  •{  Sand,  .54  ton,  at  50  cts 27 

na        |  Granite  fragments,  .57  yds.  at  70  cts.  ...  40 

|^  Gravel,  .54  ton,  at  50  cts 27 

T    ,        C  Making  mortar,  .38  yds.  at  39  cts 14| 

'  (  Making  concrete,  &c 59 

Cost  per  cubic  yard, $2  76| 

The  analyses  include  in  the  "  making  concrete, 
&c."  the  pay  of  a  superintending  mason,  and 
the  removal  of  the  material  from  the  bed  where 
it  is  made,  to  the  top  of  the  arch,  the  horizontal 
distance  averaging  200  feet,  and  the  vertical 
height,  to  which  it  was  raised  by  the  derrick,  or 
machine  for  hoisting,  about  25  feet. 
Application  196.  Before  the  application,  the  surface  of  the 
concrete!  arch  was  brushed,  moistened  with  water,  and 
well  coated  with  a  portion  of  the  same  mortar  as 
that  used  in  making  the  concrete,  care  being 
taken  to  plaster  only  that  part  which  is  to  be 
covered  immediately.  When  it  was  possible  to 
wheel  the  concrete  to  its  place,  it  was  always 
preferable  to  do  so  ;  when  this  was  impracticable, 
it  was  raised  to  the  top  of  the  arch,  by  means  of 
the  boom  derricks.  The  common  mortar-box 
was  employed  for  this  purpose,  with  advantage, 
and  when  brought  into  the  right  position,  was 
always  upset  immediately,  with   the    aid  of  a 


CONCRETE    AND    ITS    APPLICATIONS.  121 

simple  contrivance  (Fig.  4,  Plate  VII.)  without 
being  detached  from  the  arm  of  the  derrick. 

The  cheaper  concrete  was  first  put  in  place, 
and  rammed  in  successive  layers  of  six  or  eight 
inches,  until  a  certain  portion  of  the  arch  was 
completed  to  within  six  inches  of  the  intended 
surface,  when  the  outer  coat  of  cement  concrete 
was  added,  while  the  substratum  was  still  fresh, 
and  a  coating  of  stucco  at  once  applied  to  finish 
the  roofing.  As  soon  as  this  coating  had  "  set," 
it  was  covered  with  damp  sea-weed,  which  was 
kept  in  place  for  several  weeks.  When  the  depth 
of  the  concrete  would  permit,  rough  blocks  of 
rubble,  large  "cobble  stones"  and  the  like,  were 
scattered  about  in  different  parts  of  the  mass,  and 
well  imbedded  in  it,  with  the  view  of  diminish- 
ing the  cost  as  much  as  possible. 

197.  In  applying   the   concrete,    the  method   Forming 

r.r     i  ,  ,        ridges  and 

usually  practised  was  to  complete  at  once  the  gutter. 
whole  space  comprised  between  two  adjoining 
ridges.  With  this  view,  before  commencing 
operations,  a  two  inch  planking  was  set  on  edge 
along  each  ridge  ;  its  width  was  equal  to  the  in- 
tended height  of  the  ridge  above  the  arch,  and  it 
was  firmly  braced  on  the  outside.  This  being 
done,  the  gutters  of  the  arch  were  first  filled  with 
concrete  throughout  their  whole  length,  to  within 
about  eighteen  inches  of  the  intended  surface,  and 
covered  temporarily  with  wet  sail-cloths  to  pro- 
tect them  from  the  drying  action  of  the  sun. 
The  workmen  then  commenced  at  the  upper 
end  of  the  gutter,  and  completed  the  two  half- 
arches  from  ridge  to  ridge,  first  using  the  cheap 
or  common  roofing  beton,  and  finishing  the  ope- 
ration with  the  more  costly  composition,  as  before 
described.  The  slopes  and  gutters  were  fashioned 
by  means  of  straight  edges  applied  when  con- 
11 


122 


TKEATISE    ON    MORTARS. 


venient,  or  with  the  aid  of  a  common  "  mason's 
line."  It  is  very  desirable  to  apply  the  last  coat 
of  concrete  while  the  substratum  is  yet  moist ; 
and  if  any  part  of  a  previous  application  is  allowed 
to  become  dry,  care  must  be  taken  to  smear  it  well 
with  mortar  before  a  new  portion  of  concrete  is 
added,  in  order  that  there  may  be  perfect  adhe- 
sion between  the  two.  The  coating  of  stucco 
should  always  be  applied  as  soon  as  the  last  coat 
of  concrete  is  in  place. 

When  the  space  between  the  two  ridges  was 
completed,  the  planking  was  removed  to  the  next 
arch,  and  the  operation  carried  on  as  before,  care 
being  taken  to  smear  well  with  mortar  the  ver- 
tical surface  of  beton  at  the  ridge  previously 
formed.  When  the  surface  of  the  stucco  became 
sufficiently  dry,  it  was  usually  covered  with  a  thin 
coat  of  coal  tar,  designed  as  a  temporary  protec- 
tion against  the  frosts  of  winter,  until  the  arches 
could  be  covered  with  asphalte. 
Remarks.  198.  The  concrete  has  not  been  in  position  a 
sufficient  number  of  years,  to  test  fully  its  quali- 
ties ;  but  so  far  as  experience  at  Fort  Warren  ex- 
tends, the  results  obtained  by  the  foregoing  pro- 
cesses have  been  very  favorable.  When  the  use 
of  concrete  was  first  commenced  at  the  work, 
the  mortar  employed  was  but  slightly  moist, 
almost  without  coherence,  and  the  concrete  was 
applied  in  a  state  as  dry  as  possible,  the  rule 
being,  however,  that  the  mass  should  merely 
give  out  moisture  under  the  heavy  blows  of  the 
rammer.  Several  experiments  were  made  with 
it  in  the  above  condition,  and  the  result,  in  every 
case,  was  exceedingly  unfavorable,  the  concrete 
never  acquiring  any  coherence.  This  course, 
therefore,  was  at  once  abandoned,  and  the  con- 
sistence recommended  by  subsequent  experience 
is  that  described  in  Article  181. 


CONCRETE    AND    ITS    APPLICATIONS. 


123 


There  should  be  as  little  moisture,  however, 
in  "concrete  for  roofings"  as  may  be  compatible 
with  that  condition,  and  whenever  the  mass  may 
chance  to  be  too  soft,  it  can  easily  be  brought  to 
the  right  state  by  the  addition  of  a  little  cement 
powder. 

199.  The  materials    heretofore    described    as    use  of 

,  .   ,  .  -   .  .      shells  in 

employed  with  mortar  in  making  concrete  at  concrete. 
Fort  Warren,  were  broken  stone,  broken  bricks, 
or  gravel.  These  can  be  obtained  at  a  compara- 
tively cheap  rate  in  Boston  Harbor.  At  other 
localities,  shells  have  been  substituted  with  econ- 
omy and  success.  Capt.  Barnard,  of  the  corps  of 
engineers,  who  is  now  in  charge  of  Fort  Liv- 
ingston, Louisiana,  employs,  in  making  concrete, 
a  shell  known  in  that  neighborhood  as  the  cockle- 
shell. It  is  similar  in  form  to  the  clam  shell, 
though  smaller,  its  longer  dimension  averaging 
only  one  and  a  quarter  inches.  It  is  necessary 
to  screen  and  wash  the  cockle-shells  before  they 
can  be  used,  as  they  are  not  found  clean  in  any 
large  quantities. 

The  common  oyster-shells,  also,  have  been, 
sometimes,  advantageously  used  alone  or  mixed 
with  the  cockle-shells,  in  the  manufacture  of 
concrete.  Besides  the  above,  there  are  broken 
shells,  found  in  great  abundance  on  the  southern 
coast,  which  it  will  be  often  useful  to  employ  for 
a  similar  purpose.  They  consist,  for  the  most 
part,  of  fragments  of  oyster  shells,  not  exceeding 
the  finger-nail  in  size,  and  reduced  to  this  state 
by  the  action  of  the  weather,  or  the  sea.  These 
small  shells  are  mingled  in  proper  proportions 
with  the  mortar,  and  the  mixture  thus  formed 
used  alone,  or  more  generally,  to  fill  up  the  voids 
of  the  larger  shells.  The  proportions  recom- 
mended by  Capt.  Barnard,  are  three  measures  of 


124  TREATISE  ON  MORTARS. 

mortar,  four  of  the  fine  shells,  and  eight  of  the 
cockle  shells. 

Concrete,  prepared  with  the  shells  above-men- 
tioned, has  been  used  to  a  considerable  extent, 
in  the  foundations  and  superstructure  of  the  scarp 
■wall  at  Fort  Livingston.  That  in  the  founda- 
tions, which  are  often  under  water,  has  acquired 
in  two  years  almost  the  hardness  of  stone.  The 
concrete  of  the  superstructure  also  has  not  under- 
gone the  slightest  disintegration,  and  seems  to 
bear  exposure  to  the  weather  better  than  bricks, 
unless  they  are  of  the  hardest  quality.* 
Foundingin  200.  The  employment  of  concrete  is  very  ad- 
vantageous in  the  foundations  of  constructions 
in  water,  because  it  dispenses  with  the  necessity 
of  drawing  off  the  water,  always  an  expensive 
operation,  and  giving  rise,  by  the  difference  of 
pressure  which  it  produces,  to  currents  which 
dilute  and  wash  away  the  mortar.  In  founding 
with  concrete,  the  place  where  the  work  is  to  be 
laid,  is  surrounded  with  sheet  piles  of  suitable 
strength,  driven  to  a  depth,  a  little  greater  than 
the  level  at  which  the  work  is  to  be  commenced. 
The  earth  is  then  removed,  and  the  concrete  de- 
posited in  small  quantities  and  in  layers.  When 
it  reaches  the  level  of  the  surface  of  the  water, 
it  is  left  for  a  season,  until  it  becomes  sufficiently 
hard  to  sustain  the  superstructure.  If,  for  any 
reason,  the  foundation  is  not  brought  quite  to 
the  surface,  the  water  may  be  partially  drawn  off, 
in  order  to  lay  upon  the  concrete  the  first  courses 
of  masonry.  If  the  ground  is  consistent,  and 
the  concrete  is  to  be  carried  only  to  a  small  depth, 
the  piling  may  be  dispensed  with,  and  it  will 
suffice  to  dig  out  the  earth,  of  a  proper  form,  and 

*  Letter  of  Capt.  Barnard. 


CONCRETE    AND    ITS    APPLICATIONS.  125 

to  the  proper  depth.  Lastly,  if  the  ground  be 
bad,  and  the  foundations  deep,  it  will  be  neces- 
sary to  support  the  upper  part  of  the  piling,  to 
prevent  its  yielding  to  the  pressure  of  the  earth. 

The  concrete  must  not  be  thrown  to  its  place 
by  means  of  the  shovel,  nor  even  with  the  aid 
of  a  hopper,  but,  in  every  case,  should  be  low- 
ered gradually  and  deposited  gently  ;  and  an 
important  precaution  to  be  observed,  while  it  is 
passing  through  the  water,  is  to  prevent  as  much 
as  possible  any  decided  currents  within  the  en- 
closure, as  these  would  wash  away  part  of  the 
mortar.  Especial  care  should  be  taken,  to  make 
in  the  piling,  near  the  surface  of  the  water,  an 
opening  of  proper  size,  so  that  the  water  may  be 
at  the  same  level  both  within  and  without ;  other- 
wise, veins  of  water  might  be  produced,  which 
would  be  very  injurious.  Sometimes,  where  the 
foundations  are  to  be  laid,  there  are  springs  of 
water  which  drench  the  concrete  and  prevent  its 
setting ;  in  this  case,  a  simple  means  of  remedy- 
ing the  difficulty,  would  be  to  stretch  a  strong 
tarred  canvass  over  the  springs. 

While  the  concrete  is  passing  through  the 
water,  a  pulpy  fluid  usually  rises  from  its  surface, 
and  when  the  mass  is  of  any  depth,  this  drowned 
mortar,  which  sets  imperfectly,  may  interpose 
itself  between  the  layers,  and  break  their  con- 
tinuity. Perhaps  the  best  means  of  getting  rid 
of  this  injurious  matter,  would  be  one  or  two 
powerful  pumps,  by  working  which  it  might  be 
removed  as  fast  as  it  rises. 

There  are  several  modes  of  transmitting  con- 
crete through  the  water,  probably  none  more 
convenient  than  the  following,  used  at  Strasburg. 
A  sort  of  spoon,  made  of  strong  sheet  iron,  was 
employed  for  the  purpose.  It  was  twenty  inches 
11* 


TREATISE    ON    MORTARS. 

long  and  sixteen  inches  wide,  with  a  flat  bottom  ; 
at  the  sides,  and  at  the  back,  the  iron  was  turned 
up  square  to  the  height  of  six  inches,  but  not  at 
the  front  edge,  which  was  merely  curved  upward 
a  little.  The  spoon  was  furnished  with  a  handle, 
resembling  that  of  an  ordinary  water-pail,  with  a 
ring  in  the  middle.  The  ring  was  suspended  on 
an  iron  hook,  connected  by  a  socket  with  a 
wooden  handle,  so  that  the  spoon  was  movable 
about  the  point  of  suspension,  but  maintained 
itself  in  a  horizontal  position,  when  filled  with 
concrete.  By  means  of  the  long  wooden  handle, 
it  was  let  down  to  the  required  place,  when  on 
pulling  a  string,  attached  to  the  back  of  the  spoon, 
it  was  upset,  the  concrete  fell  out,  and  the  spoon 
was  withdrawn,  to  be  again  used  in  the  same 


way 


* 


Modifying      201.  In  founding  with  concrete  in  deep  water, 

constitu-  a  <•     i 

ent3.  there  should  be  some  modification  of  the  propor- 
tions of  the  constituents,  as  the  mortar  must  not 
only  become  hard  after  a  time,  but  should  set 
speedily.  In  order  to  attain  this  end,  it  ought  to 
be  composed  of  sand  and  hydraulic  cement  only 
(no  lime),  with  a  much  larger  proportion  of  the 
cement  than  will  suffice  to  fill  the  voids  of  the 
sand.  The  quantity  of  the  mortar,  too,  in  the 
concrete,  should  be  so  increased,  that  the  frag- 
ments may  be  imbedded  by  their  own  weight, 
as  the  use  of  the  rammer  would  be  decidedly 
injurious,  and  the  only  reliance  is  upon  the  gentle 
operation  of  the  rake  or  other  levelling  instru- 
ments, and  the  pressure  of  the  superincumbent 
mass. 
Economy  202.  In  order  to  illustrate  the  economy  of  using 
concrete  in  constructions,  I  will  annex  a  compara- 


lii  usin 
concrete 


*  Totten's  Treussart,  pp.  109,  125. 


CONCRETE    AND    ITS    APPLICATIONS.  127 

tive  view  of  the  cost  of  different  kinds  of  masonry 
at  Fort  Warren. 

Rubble  masonry,  dry.  costs  per  cubic  yard,  about     $3  00 
Rubble  masonry,  laid  in  mortar,  4  25 

Brick  masonry,  per  cubic  yard,  6  25 

Facing  stone,  sea-wall,  beds  and  joints,  hammered,     9  00 
Concrete,  least  costly  kind,  a  little  over  2  00 

Concrete,  most  costly  kind,  a  little  over  3  50 

From  the  above  table,  as  well  as  from  the 
analyses  in  other  parts  of  this  chapter,  it  is  seen 
at  once,  how  great  a  saving  in  the  cost  of  masonry 
is  effected  by  the  employment  of  concrete. 


128  TREATISE  ON  MORTARS, 


CHAPTER    VIII. 

THEORY  OF  THE  SOLIDIFICATION  OF  MORTARS. 

Remarks.  203.  The  solidification  of  mortars  has  been 
long  a  subject  of  controversy,  and  many  singular 
theories  have  been  published  on  the  subject.  My 
limits  will  not  permit  me,  however,  to  dwell  upon 
these,  and  I  will  confine  myself,  in  what  follows, 
to  a  brief  mention  of  the  most  rational  hypoth- 
eses. 
induration  204.  The  induration  of  mortars  was  first  at- 
to  what '  tributed  to  the  slow  and  successive  action  of  the 
'buted""  carbonic  acid  of  the  atmosphere  ;  and  this  expla- 
nation was  universally  received  for  a  long  time.* 
It  has,  however,  been  recently  rejected  by  several 
distinguished  writers,  probably  in  consequence  of 
their  not  classing  in  distinct  categories,  the  rich 
and  hydraulic  limes.  For  there  can  be  no  doubt, 
that  ordinary  mortars  (which  do  not  set),  are  very 
much  improved  by  the  absorption  of  carbonic 
acid  ;  a  fact,  which  may  be  easily  proved  by 
comparing  the  resistance  of  the  interior  of  a  large 
mass  of  ordinary  mortar,  twelve  months  old,  with 
that  of  its  superficial  crust. 

In  hydraulic  mortars,  however,  the  induration 
appears  to  be  due  to  other  causes,  for  they  often 
set  immediately,  and  will  harden  none  the  less 
rapidly,  if  immersed  in  distilled  water  and  ex- 
cluded from  all  contact  with  the  air.f 

It  will,  therefore,  be  advisable,  in  accounting 

*  Smith's  Vicat,  p.  125.— Totten's  Treussart,  p.  105. 
t  Totten's  Treussart,  p.  106. 


mor- 
tars. 


SOLIDIFICATION    OF    MORTARS.  129 

for  the  solidification  of  mortars,  to  separate  the 
simple  from  the  compound  ;  and  with  this  view, 
I  will  take  up  in  succession,  the  "  ordinary " 
mortars,  the  pouzzolana  mortars,  and  the  mortars 
made  of  hydraulic  lime  or  cement. 

205.  When  fat  lime  is  immersed  in  water,  it  soiidifica- 
absorbs  rapidly  a  quantity  of  the  liquid  equal  to  dln0anry° ' 01 
nearly  0.22  of  its  weight.  Withdrawn  then 
immediately  and  left  in  contact  with  the  air,  it 
slakes  with  disengagement  of  heat,  and  falls  into 
an  impalpable  powder.  The  hydrate  of  lime  is 
thus  formed,  and,  as  its  molecules  are  too  far 
apart  to  unite  into  a  compact  mass,  it  is  always 
brought  to  the  state  of  paste,  in  order  to  be  used 
in  making  mortar.  Now  this  paste,  as  has  been 
previously  remarked,  if  kept  from  contact  with 
the  air,  will  remain  soft  for  an  indefinite  period ; 
and  this  too  will  be  the  case,  even  if  it  be  mixed 
with  any  of  the  inert  sands  ;  a  fact  proved  by 
the  examinations  of  thick  masonry,  two  hundred 
years  old.  But  every  day's  experience  shows, 
that  if  the  lime  or  mortar  be  left  in  free  contact 
with  the  air,  it  will  solidify  ;  and  Petot  states  that 
the  solidification  will  take  place  with  great  rapid- 
ity, if  the  air  be  replaced  with  pure  carbonic  acid 
gas.  In  either  case,  the  same  writer  further  re- 
marks, the  absorption  of  the  acid,  extending 
gradually  from  the  surface  to  the  centre  of  the 
specimen,  would  continue  to  progress,  until  the 
acid  is  to  the  base,  in  the  ratio  of  44  to  56,  as  in 
the  natural  carbonate  of  lime.  But  the  propor- 
tion of  water,  existing  in  the  hydrate  of  lime,  is 
not  rejected,  and  the  resulting  carbonate  differs 
from  the  natural  carbonate,  in  being  what  may 
be  termed  a  double  salt,  the  hydrocarbonate  of 
lime. 

The  foregoing  being  premised,  it  appears,  that 


130  TREATISE  ON  MORTARS. 

for  the  solidification  of  fat  lime,  1st.  the  propor- 
tion of  water  must  be  greater  than  in  the  dry 
hydrate  ;  2d.  there  should  be  contact  of  the  air, 
or  better  still,  of  pure  carbonic  acid  gas  j  3d.  the 
mixture  of  quartzose  sand,  without  the  contact 
of  the  air  would  have  no  influence.  Hence 
comes  the  superiority  of  common  lime,  slaked 
spontaneously  and  already  somewhat  carbonated  ; 
and  hence,  too,  the  impossibility  that  "  ordinary  " 
mortars  should  harden  in  the  interior  of  thick 
masonry,  or  under  water,  since  water  in  general 
contains  only  inappreciable  quantities  of  carbonic 
acid  in  solution.* 
Pouzzoiana     206.  Gen.  Treussart  explains  the  hardening  in 

mortars.  ,-T  . 

water,  of  mortars  made  with  fat  lime  and  pouzzo- 
iana, by  supposing  a  chemical  combination  be- 
tween these  two  substances,  and  in  proof  of  this 
view  made  the  following  experiment,  which  ap- 
pears to  be  conclusive.  He  took  a  piece  of  mor- 
tar, from  the  centre  of  a  mixture  composed  of 
one  part  of  lime  from  white  marble,  and  two 
parts  of  pouzzoiana,  which  had  been  lying  a  year 
in  water,  reduced  it  to  a  fine  powder,  and  then 
placed  it  in  a  vessel  filled  with  distilled  water. 
Now  if  fat  lime  be  immersed  in  water,  about  g-^ 
of  its  weight  will  be  dissolved  in  a  few  minutes. 
Nevertheless,  after  twenty-four  hours,  the  distilled 
water  contained  no  portion  of  the  lime,  and  neither 
had  the  latter  passed  to  the  state  of  a  carbonate, 
for  on  pouring  muriatic  acid  upon  the  powdered 
mortar,  little  or  no  effervescence  took  place. 

The  lime  had  not  become  carbonated,  and  yet 
would  not  dissolve  in  water  :  the  inference,  there- 
fore, was  unavoidable,  that  it  must  be  in  a  state 
of  combination  with  the  pouzzolana.f 

*  Totten's  Treussart,  p.  197.  t  Totten's  Treussart,  p.  107. 


SOLIDIFICATION    OF    MORTARS.  131 

207.  The  constituent  element  of  pouzzolana,  Remarks. 
which  enables  it  to  form  a  hydraulic  compound 

with  fat  lime,  is  probably  the  same  substance  as 
that  which  imparts  energy  to  the  hydraulic  limes  ; 
and  I  will,  therefore,  reserve  what  I  have  to  say 
upon  this  question,  for  the  succeeding  Article. 

208.  It  is  not  necessary  to  suppose,  in  order  to  Mortars  of 
account  for  the  hardening  under  water  of  mor-  iuL ore*, 
tars,  made  of  hydraulic  lime  or  cement,  and  sand,     raent- 
that  there  is  any  combination  between  these  sub- 
stances, as  has  been  assumed  by  some  authors  ; 
inasmuch  as  the  cementing  material  alone,  with- 
out any  addition  of  other  matters,  possesses  this 
indurating  property.     We  have  merely,  then,  to 
enquire  the  cause  of  the  subaqueous  solidifica- 
tion of  the  hydraulic  limes  and  cements. 

Bergman,  perhaps  the  first  chemist  who  gave 
the  analysis  of  a  hydraulic  limestone,  attributed 
the  virtue  of  the  lime  resulting  from  its  calcina- 
tion, to  the  presence  of  a  few  hundredths  of  the 
oxide  of  manganese.  Guyton  de  Morveau,  a 
French  chemist,  who  followed  him  in  the  inves- 
tigation, was  also  of  the  same  opinion,  and  an- 
nounced further,  that  an  artificial  hydraulic  lime 
might  be  prepared  by  calcining  together  ninety 
parts  of  pulverized  limestone,  four  parts  of  clay, 
and  six  parts  of  the  black  oxide  of  manganese. 

Smeaton,  the  English  engineer,  had  remarked, 
however,  as  early  as  1756,  the  curious  fact,  that 
the  existence  of  clay  in  a  calcareous  stone,  gave 
it  the  property  of  indurating  under  water.  Never- 
theless, the  notion  that  the  oxide  of  manganese 
was  the  essential  element,  continued  to  prevail, 
until  Saussure  discovered,  that  the  lime  of  Cha- 
mouni,  though  entirely  destitute  of  manganese, 
contained  the  property  in  question,  and  he  thence, 
with  reason,  inferred,  that  it  depended  not  upon 


132  TREATISE  ON  MORTARS. 

manganese,  but  upon  the  clay  which  existed  in 
the  lime.  Since  that  time,  other  hydraulic  lime- 
stones have  been  analyzed  without  yielding  any 
manganese,  and  but  few  persons  now  entertain 
the  opinion,  that  this  substance  possesses  of  itself 
any  useful  qualities,  as  a  hydraulic  ingredient. 

In  order  to  settle  the  doubts  which  existed 
upon  this  question.  Mr.  Vicat,  in  1817,  determined 
to  proceed  synthetically,  and  compound  hydraulic 
limes  at  once,  by  calcining  mixtures  of  common 
lime  and  clay  ;  and  the  experiments  which  he 
performed  were  attended  with  very  successful 
results.  They  proved  conclusively,  that  the 
addition  of  clay  imparted  hydraulic  virtues  to 
fat  lime,  and  manufactories  for  making  hydrau- 
lic limes  in  the  large  way,  out  of  those  two  sub- 
stances, have  been  subsequently  established.* 

Whether,  however,  of  the  constituents  of  clay, 
the  silica  alone  was  the  important  element,  or 
whether  the  alumina  was  also  to  be  taken  into 
account,  as  well  as  the  magnesia,  which  often 
accompanies  them,  is  still  a  matter  of  some  con- 
troversy among  men  of  science. 

With  the  view  of  procuring  some  new  light 
on  this  question,  I  consulted  several  scientific 
friends,  and  Lt.  Kendrick  of  the  Artillery,  the 
assistant  professor  of  chemistry  at  the  Military 
Academy,  was  kind  enough  to  perform,  at  my  in- 
stance, a  series  of  experiments,  attended  with  the 
interesting  results,  recorded  hereafter.  The  time 
to  which  he  was  limited,  however,  was  so  short, 
that  he  was  not  enabled  to  complete  his  investi- 
gations, and  the  subject  still  affords  an  ample  field 
for  experimental  research. 

In  making  the  several  trials,  the  materials  em- 

*  Totten's  Treussart,  pp.  3,  4,  5. 


SOLIDIFICATION    OF    MORTARS.  133 

ployed  were  either  prepared  by  himself,  or  the 
perfect  purity  of  those  at  hand  was  secured.  The 
ingredients  of  each  composition  were  thoroughly 
mixed  together,  by  means  of  the  mortar  and 
pestle,  and  in  the  proportions  stated  in  the  table. 
If  lime  or  magnesia  was  used,  it  was  previously 
slaked  with  hot  water  ;  if  the  carbonate  of  either 
was  employed,  it  was  moistened,  and  the  mate- 
rial in  each  case  was  subsequently  heated  in 
platinum  crucibles,  open  but  in  a  closed  stove. 
After  the  heating  was  over,  the  hydrates  were 
treated,  as  indicated  in  Article  18. 

The  comparative  hardness  was  ascertained  by 
placing  weights  upon  a  test  needle  2V  of  an  inch 
in  diameter,  which  was  held  firmly  in  a  vertical 
position  ;  and  the  specimens  were  submitted  to 
trial  without  being  removed  from  the  vessels 
containing  them. 

As  a  single  successful  experiment,  with  any 
material  known  to  be  pure,  will  prove  that  it  pos- 
sesses hydraulic  properties,  it  was  preferred  to 
seek  good  results  with  various  substances,  rather 
than  to  make  a  series  of  comparative  trials  with 
two  or  three,  in  different  proportions,  and  exposed 
to  different  degrees  of  heat.  This  will  explain 
any  apparent  want  of  sequence,  in  the  results 
which  I  will  proceed  to  transcribe,  with  some 
unimportant  omissions,  from  Lieut.  Kend  rick's 
letter. 


12 


134 


TREATISE     ON    MORTARS. 


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20 

41 

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100 

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loo 

red 

451 

SOLIDIFICATION    OF    MORTARS.  135 

In  addition  to  the  above,  a  series  of  experi- 
ments was  performed  by  Lt.  Kendrick,  with  the 
view  of  testing  the  hydraulic  virtues  of  the  oxide 
of  manganese,  but  in  no  instance,  where  this 
substance  was  mingled  with  pure  lime,  did  he 
succeed  in  obtaining  any  good  result,  nor  was  he 
more  fortunate  in  substituting  pure  magnesia  in 
the  place  of  the  oxide  of  manganese  ;  as  appears 
from  the  table,  Nos.  23,  24,  25,  27,  28,  42.  There 
is  a  strong  presumption,  therefore,  that  neither 
manganese  nor  magnesia  will  of  itself  impart 
hydraulic  qualities  to  fat  lime.  So  far  as  mag- 
nesia is  concerned,  this  view  is  opposed  to  that 
of  Yicat  ;  but  it  seems  probable,  that  in  those 
cases  mentioned  by  him,  in  which  he  appeared 
to  obtain  different  results  with  lime  and  magnesia, 
the  materials  employed  were  not  entirely  pure. 
A  single  successful  experiment,  however,  with 
either  manganese  or  magnesia  and  fat  lime,  the 
materials  being  proved  to  be  pure,  will  show  this 
inference  to  be  erroneous. 

The  positive  results  exhibited  in  the  table,  are 
more  to  be  relied  on  and  lead  to  more  safe  con- 
clusions.    The  examination  of  them  shows  : 

1st.  That  silica  and  lime  employed  together, 
without  any  other  admixture,  will  give  a  hy- 
draulic compound.  Nos.  3,  8,  9,  11,  13,  34, 
35,  36. 

2d.  That  silica,  alumina  and  lime  will  produce 
an  equally  energetic  composition.  Nos.  1,  4,  6, 
7,  16,  37,  3S,  39.  In  some  respects,  the  addition 
of  alumina  improves  the  mixture.  Being  inso- 
luble in  water,  it  protects  the  outer  portions  of 
the  lime  from  solution,  until  the  union  of  the 
latter  with  the  silica  is  effected,  and  prevents  the 
free  permeation  of  water  through  the  mortar, 
which  might  greatly  injure  its  quality. 

3d.  That  silica,  alumina  and  magnesia,  will 


136  TREATISE    ON    MORTARS. 

from  a  good  hydraulic  compound,  without  the 
addition  of  lime,  Nos.  10,  17,  18,  19. 

This  fact  may  account  for  the  existence  of  hy- 
draulic qualities  in  the  native  carbonate  of  mag- 
nesia, which,  like  the  carbonate  of  lime,  may 
frequently  contain  a  portion  of  clay  in  its  com- 
position. 

4th.  That  silica,  lime  and  magnesia  give  a 
better  hydraulic  result,  than  silica  and  lime, 
Nos.  11,  12,  13,  14.  This  probably  arises  from 
the  formation  of  double  silicates,  the  silicic  acid 
uniting  with  both  lime  and  magnesia. 

Nos.  21,  22,  41,  exhibit  surprising  results,  and 
lead  to  the  inference  which  is  generally  deduci- 
ble  from  the  table,  that  the  induration  of  hy- 
draulic mortars  is  not  to  be  ascribed  to  any  one 
agent,  nor  ever  to  precisely  the  same  causes ; 
though,  in  most  cases,  it  is  owing  to  the  formation 
of  a  silicate. 

With  the  view  of  discovering  the  constituents 
of  some  of  our  hydraulic  limes,  I  submitted  for 
analysis  to  Dr.  Jackson  of  Boston,  two  specimens 
of  limestone,  obtained  from  different  localities  and 
possessed  of  different  properties.  They  both  fur- 
nish after  calcination,  products,  which  it  is  neces- 
sary to  pulverize,  in  order  to  prepare  them  for  use, 
and  are  both  known  in  commerce,  as  hydraulic 
cements;  one  called  Barnes's  Connecticut  Cement 
from  Southington,  Conn.,  the  other,  Lawrence's 
Rosendale  Cement,  from  the  vicinity  of  Rondout, 
New  York. 

The  first  was  inferior  in  quality  to  many  hy- 
draulic limes,  although  sometimes  quite  energetic. 
A  portion  of  the  cement  being  converted  into 
paste  and  placed  in  a  tumbler  of  water,  cracks 
invariably  showed  themselves  upon  its  surface, 
and  being  remixed  and  again  immersed,  it  re- 
quired from  ten  days  to  a  fortnight  to  become 


SOLIDIFICATION    OF    MORTARS. 


137 


hard.  The  Rosendale  cement,  on  the  other  hand, 
was  quite  energetic,  setting  under  water  in  five 
minutes  after  immersion,  though,  like  the  cement 
from  Connecticut,  its  energy  had  probably  been 
somewhat  impaired,  since  it  had  left  the  kiln. 

The   results   of    the   two    analyses   were   as 
follows : — 

One  hundred  grains  of  the  Connecticut  cement,  being  thoroughly 
dried  at  212°  F.  yielded  on  chemical  analysis: — 

'Siliceous  &  ferruginous  sand,  8.780  grs. 

Oxygen. 

Silicic  acid, 23.620  12.275) 

Carbonic  acid, 8.000  5.788  >  18.135. 

Sulphuric  acid, 0.137  0.072  ) 

Lime, 47.285  13.281 5 

Alumina, 6.120  2.941 

Peroxide  of  iron,    ....     3.260  0-998liaiQn 

Magnesia, 1.920  0.760  f10-lJU- 

Manganese  (oxide  of),    .     .     0.100  0.077  { 

Potash, 0.792  0.133J 


100.014 
014 


18.190 
jain,  ashes. 


100.000 
Oxygen  of  the  acids  =  18.135 
Oxygen  of  the  bases  =  18.190. 

One  hundred  grains  of  the  Rosendale  cement  yielded  on  analy- 
sis, as  follotcs : — 


Silicic  acid, 
Sulphuric  acid, 
Carbonic  acid, 
Lime,      .     .     . 
Magnesia,   .     . 
Alumina,     .     . 
Peroxide  of  iron, 
Oxide  of  manganese 
Potash,  .... 
Soda,       .... 
Water 


18.170 
1.000 
4.000 
44.970 
19.080 
5.500 
4.900 
1.000 
0  673 
0.438 
0.200 


grs.  con. 


Oxygen. 

9.439  ) 

0.598  >  12.93. 

2.893  ) 
12.630 

7.360  T 

2.563 

1.501 

0.464  i  12.291. 

0.114  | 

0.112  | 

0.177J 


99.931 

The  oxygen  of  the  acids  is,  12.930 

"        "         "     "  lime   "  12.630 

"         "         "     «  other  bases  is,  12.291 

*  The  sand  is  not  in  chemical  combination,  but  is  mechanically 
mixed  with  the  other  ingredients  of  the  cement. 

12* 


138  TREATISE  ON  MORTARS. 

From  which  it  would  seem  that  bibasic  com- 
pounds are  formed  when  the  cement  sets. 

On  comparing  the  analyses  with  each  other,  it 
appears  that  the  chief  constituents  of  the  Con- 
necticut cement  are  silica  and  lime,  whereas  a 
large  proportion  of  magnesia  enters  into  the  com- 
position of  the  Rosendale.  The  inference  sug- 
gested by  the  results  of  the  table  is  thus  strength- 
ened by  those  of  the  analyses,  viz.,  that  the 
increased  energy  of  the  latter  cement  may  be 
ascribed  to  the  formation  of  double  silicates. 

Dr.  Jackson,  who  has  performed  many  experi- 
ments with  hydraulic  mixtures,  informs  me,  that 
the  oxide  of  manganese  will  answer  the  same 
purpose  as  magnesia :  which  is  not  surprising,  as 
the  two  substances  are  isomorphous  with  each 
other. 

Professor  W.  B.  Rogers,  of  the  University  of 
Virginia,  has  analyzed  within  the  last  six  years 
upwards  of  a  hundred  specimens  of  cement  rocks 
derived  from  the  carboniferous  and  Appalachian 
series  of  Virginia  and  other  States ;  and  he  believes 
the  cause  of  the  solidification  of  the  products, 
obtained  by  calcining  both  those  classes  of  rocks, 
to  be  the  formation  of  silicates :  in  the  former 
chiefly  those  of  lime  and  oxide  of  iron,  in  the 
strikingly  hydraulic  Appalachian  limestones, 
those  of  lime  and  magnesia. 

209.  The  following  table,  extracted  from  the 
recently  published  report  of  the  Geological  Survey 
of  New  York,  will  show  the  composition  of 
various  hydraulic  limestones  of  that  State. 


SOLIDIFICATION    OF    MORTARS. 


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INDEX. 


Pages. 


Absorption  of  carbonic  acid  and  moisture,  by  limes  exposed 

to  the  atmosphere,  Art.  7, 40,             .         .         .         .  2, 20 
Acids,    action    of,    on    carbonates    of  lime    and    magnesia, 

Art.  15,  25, 5,  11 

Adhesiveness  of  mortars,  how  estimated,  Art.  98  to  101,     55  to  58 

Air,  deterioration  of  hydraulic  limes  by  the  action  of,  Art.  40,  20 

influence  of  the  contact  of,  in  the  manufacture  of  Pouz- 

zolana,  Art.  69,           .......  36 

Arenes,  meaning  of  the  term,  Art.  59,            ....  31 

used  as  a  pouzzolana,  Art.  59,       .....  31 

physical  characters  of,  Art.  60,      .....  32 

improved  by  calcination,  Art.  61,           ....  32 

Argillaceous  limestones,  kilns  for  burning,  Art.  108  to  121,   62  to  72 


B. 

Bertiiier,  M.,  his  method  of  analyzing  limestones,  Art.  21,  8 

Beton,  meaning  of  the  term,  Art.  169,            ....  106 

Bricks,  dust  of,  used  as  a  Pouzzolana,  Art.  70,       ...  36 

number  of,  stuck  together  with  hydraulic  cement  and 

projecting  from  the  6ide  of  a  wall,  Art.  99,         .         .  56 

fragments  of,  used  in  making  concrete,  Art.  170,           .  106 

Brinel,  Mr.,  his  experimental  semi-arches,  Art.  100,    .         .  56 


C. 

Calcareous  incrustations  in  using  trass,  Art.  58, 

minerals,  tests  to  discover  them,  Art.  1,  4,  15, 

Calcination  of  limestone  in  the  large  way,  Art.  106, 
conditions  to  render  it  easy,  Art.  107, 
various  kilns  for,  described,  Art.  108  to  117, 
time  required  for,  Art.  115, 
average  quantity  of  combustibles  in,  Art.  118, 

Carbonate  of  lime,  chemical  constitution  of,  Art.  1, 
of  magnesia,  value  as  a  cement,  Art.  25, 


30 
1,  2,  5 
61 
61 
72 
67 
Til 
1 
11 


62  to 


142 


INDEX. 


Carbonic  acid,  of  the  atmosphere,  absorbed  by  lime,  Art.  7, 
increases  the  hardness  of  limes,  Art.  204, 
solidification  of  mortars  attributed  to  the  slow  and  suc- 
cessive action  of,  Art.  205,     ...... 

Cement,  hydraulic,  improperly  called  Roman,  Art.  42, 
proof  of  its  excellence,  Art.  98  to  103, 
See  Hydraulic  Cement. 

Clays,  nature  of,  Art.  Go,        .         .         .... 

used  as  pouzzolanas,  Art.  66,         .... 

mode  of  examining  and  testing  qualities  of,  Art.  67,  68, 
best  kind  of,  for  making  artificial  lime,  Art.  124, 

Coal,  bulk  of,  used  in  burning  limestone,  Art.  118, 

Composition  of  mortars,  Art.  73  to  90, 

Concrete,  meaning  of  the  term,  Art.  169,     . 
materials  used  in  making,  Art.  170, 
principle  in  fixing  proportions  for,  Art.  171, 
English  mode  of  preparing,  Art.  172,    . 
for  foundations  of  sea-walls,  Art.  175  to  182, 
for  foundations  of  scarp-wall,  Art.  183, 
for  pintle  blocks,  Barbette,  Art.  184, 
for  foundations,  breast-height  walls,  Art.  185, 
for  superstructure,  sea-wall,  Art.  186  to  189, 
for  piers  and  scarp,  Fort  Warren,  Art.  191, 
for  roofing  casemates,  Art.  192  to  198, 
use  of  shells  in,  Art.  199,      .... 
foundations  in  water,  Art.  200, 
economy  in  using,  Art.  202, 


Pajes. 

2 

128 

.       129 

21 

55  to  59 


33 

33 

34,35 

74 

69 

38  to  50 

106 

106 

107 

107 

to  114 

114 

114 

116 

16,  117 

118 

118  to  122 

123 

124 

126 


109 


D. 

Dolomites,  useful  as  cements,  Art.  23, 

mode  of  analyzing  by  hydration,  Art.  24, 


10 
10 


E. 

Desiccation  rapid,  bad  effects  of,  upon  mortars,  Art.  88,  .  49 
Eddystone  lighthouse,  mortars  used  in  building,  Art.  90,  .  51 
Extinction.     See  Slaking,  Art.  6,  32  to  38,  .         .    2,  15  to  18 


Forge  scales,  powdered,  used  as  a  pouzzolana,  Art.  71,  .         36 

Fossil  sands,  deposits  of,  Art.  48,  .....         24 

Foundations,  use  of  concrete  in,  Art.  175  to  185, 200,    109  to  116, 124 


G. 


Girard,  M.,  remarks  upon  the  arenes,  Art.  59, 
Gravel,  how  the  voids  in  are  measured,  Art.  76,  77, 
Low  to  ascertain  proportions  in  mixing,  Art.  79, 


31 

41,42 
42 


INDEX. 


143 


Greywacke,  its  character  as  a  pouzzolana,  Art.  62, 
Grouting,  meaning  of  the  term,  Art.  168, 
Gypsum,  for  what  purpose  used,  Art.  26, 
how  distinguished,  Art.  27, 
how  tested  and  prepared,  Art.  23,  29, 


Pajes. 

32 
105 
12 
12 
13 


H. 

Hardness  of  mortars,  variations  in,  how  tested,  Art.  104, 
Heat  of  the  weather  injurious  to  mortars,  Art. 
Hydrate  of  lime,  chemical  compound,  Art.  7, 
Hydraulic  cement,  properties  of,  Art.  12, 

mode  of  testing,  Art.  19, 

stone  to  be  burned  with  care,  Art.  43, 

precautions  in  using,  Art.  44  to  47, 

how  to  restore  the  quality  of  damaged,  Art.  45,  123, 

how  to  preserve,  Art.  46, 

manufacture  of,  Art.  121,  122, 

manufacture  of,  artificial,  Art.  124,  125, 
Hydraulic  lime,  properties  of,  Art.  11, 

mode  of  testing,  Art.  18, 

remarks  upon,  Art.  31,  40,     . 

mode  of  preserving  in  the  large  way,  Art.  41, 

manufacture  of  artificial,  Art.  124,  155, 


60 

49 

2 

4 

7 

21 

22  23 

22J73 

23 

71  to  73 

74,  75 

4 

6 

15,20 

20 

74,75 


I. 

Immersion,  slaking  by,  Art.  35,  36,         ...  16,  17 

Ingredients  used  in  making  mortars,  Art.  30,  ...  14 
Iron  stone,  siftings  of,  used  as  a  pouzzolana,  Art.  71,  .  .  36 
Induration  of  mortars,  Art.  203  to  209,  .         .         .    128  to  138 


Jaghery,  meaning  of  the  term,  Art.  144, 


92 


K. 

Kendrick,    Lieut.,   experiments    with    hydraulic    mixtures, 

Art.  208,     .         .         . 132 

Kilns,  for  burning  limestone,  comprised  under  two  heads, 

Art.  108, 63 

best  form  of  "flame  kiln,"  Art.  109,  111,     .         .  63,64 

mode  of  charging  "  flame  kiln,''  Art.  110,    ...  63 

for  burning  bricks  and  lime  together,  Art.  112,      .          .  64 
adapted    to    the    calcination   of  artificial    pouzzolana, 

Art.  112, 64 

temporary,  or  "  field,"  Art.  113,            ....  65 

combination  of  coke-oven  wilh  lime  kiln,  Art.  114,      .  65 

"  perpetual,"  used  in  Yorkshire,  Art.  116,    ...  63 


144 


INDEX. 


Kilns,  conical,  Art.  117,  .... 

manner  of  charging  coal  kilns,  Art.  118, 
remarks  upon,  Art.  119,  120, 


Pages. 

68 
69 

70,71 


Lime,  one  species  only  of,  Art.  2, 1 

substances  affording,  Art.  3,  .         .         .         .         .      1, 2 

properties  of  pure,  Art.  7,     .....  2 

classification  of  limes,  Art.  8,        ....  3 

"poor"  lime,  Art.  10,  16,  31,  .  .  .  .  4,6,14 
"fat"  lime,  Art.  9,  17,  31,  39,      .         .         .  3,6,14,19 

"  hydraulic"  lime,  Art.  11,  18,  31,40,  41,    .         .  3  to  20 

relation  between  the  qualities  of  limes  and  the  chemical 

constitution  of  the  stones  whence  they  are  derived, 

Art.  22, 9 

three  modes  of  slaking,  Art.  32,  35,  37,  .  .  15  to  17 
mode  of  estimating  increase  in  bulk,  Art.  33,  .  .  16 
mode  of  preserving  caustic,  Art.  39,  41,        .         .  19,20 

when  it  is  better  to  err  from  a  deficiency  rather  than 

from  an  excess  of,  Art.  85,  .....         48 

bad   qualities  of  fat   improved  by  the  use  of  sugar, 

Art.  144, 92 

how  fat  lime  may  acquire  hydraulic  properties,  Art.  37,         17 
impotency  of  fat  on  quartz,  Art.  75,       ....         41 
Limestones,  chemical  constitution  of,  Art.  1,  ...  1 

many  varieties  of,  furnishing  each  a  different  product, 

Art.  1,2, 1 

mode  of  distinguishing,  Art.  4,  15,  .  .  .  .  2,  5 
mode  of  analyzing,  Art.  21,  .....  8 

calcination  of,  in  the  large  way,  Art.  106  to  120,  61  to  73 

magnesian,  see  Dolomites. 
Lime-water,  action  in  precipitating  magnesia,  Art.  21,  .  9 


M. 

Magnesia,  combines  with  water,  though  slowly,  Art.  23,      .  10 

how  separated  from  lime,  in  an  acid  solution,  Art.  25,  11 
Magnesian  limestones,  see  Dolomites. 
Manganese,  oxide  of,  opinions  as  to  the  virtues  of  hydraulic 

lime,  depending  on  the  presence  of,  Art.  208,       .         .  131 
Manipulation  of  mortars,  Art.  88,  89,  163,   ...          49, 102 

Marble,  chemical  constitution  of,  Art.  5,  2 
Masonry,  precautions  respecting  soaking  materials  used  in, 

Art.  168,    ...                  105 

Minion,  meaning  of  the  term,  Art.  71, 36 

used  as  a  pouzzolana,    .......  36 

Molasses,  used  to  improve  the  qualities  of  rich  lime,  Art.  144,  92 

Mortars,  ingredients  of,  Art.  30, 14 

choice  of  mode  of  slaking  lime  for,  Art.  38,         .         .  18 


INDEX.  145 

Fa?es. 


Mortars,  remarks  upon,  Art.  73,  74,      .         .         .  .        38 

general  principle  in  the  composition  of,  Art.  75,  .         39 

minimum  of  cementing  matter  required  in,  Art.  76,      .         41 
mode  of  measuring  voids  in  sands  for,  Art.  76,  77,  41,  42 

mode  of  measuring  ingredients  of,  Art.  80,  •         •         44 

best  proportion  of  cementing  matter  in,  Art.  83,  84,       46,  47 
manipulation  or  manufacture  of,  Art.  88,  89,  163,  49,  102 

used  by  Smeaton,  Art.  90, 51 

classification  of,  Art.  127, 78 

for  "  pointing,"  Art.  131  to  137,  .         .         .       82  to  87 

for  "  stucco,"  Art.  138  to  149,      .         .         .         .        87  to  95 
"  ordinary  "  (fat  lime  and  sand),  Art.  150  to  154,  95,  96 

implements  used  at  Fort  Warren  in  making,  Art.  155,  97 

machines  for  making,  described,  Art.  156,  157,  97  to  100 

at  Fort  Warren,  mode  of  slaking  the  lime  for,  Art.  153,         99 
for  stone  masonry,  Art.  160,  ..... 


101 
102 
103 
104 
104 
105 


for  brick  masonry,  Art.  162,  .... 

manipulation  of,  Art.  163,      ..... 

cost  of,  Art.  164,   ....... 

implements  for  carrying,  Art.  165, 

quantity  of,  in  cubic  yards  of  masonry,  Art.  167, 

application  of,  Art.  163,         ..... 

solidification  of,  Art.  203  to  209,  .         .        .128  to  138 

Muriatic  acid,  action  of,  on  limestones,  Art.  4,  15,       .         .      2,  5 

N. 
Nitric  acid,  action  of,  on  limestones,  Art.  4,  15,    .         .         .      2,  5 

O. 

Oxide  of  calcium,  chemical  name  of  lime,  Art.  2,  .         .  1 

Oxide  of  manganese,  see  Manganese. 


Parker's    hydraulic    cement,    improperly    termed    Roman, 

Art.  42, 21 

Pasley,  Gen.,  his  modes  of  determining  the  strength  of  mor- 
tars and  cements,  Art.  93  to  103,        .         .         .        52  to  59 
his  process  of  making  artificial  cement  in  the  large 

way,  Art.  125,    ........         75 

Paste,  volume  yielded  by  pure  quick  lime,  Art.  6,  .         .  2 

consistence  of,  in  fixing  proportions  of  ingredients  in 

mortars,  Art.  80,         ....         ...         45 

Petot,   M.,    theory    of   solidification    of   ordinary    mortars, 

Art.  205, 129 

Piers,  concrete  used  in  constructing,  Art.  191,        .         .         .       118 

Pise,  arenes  used  as,  Art.  59,  ......  31 

Plastering, see  Stucco. 

13 


146 


INDEX. 


Plaster  of  Paris,  see  Gypsum. 

Pointing,  definition  of,  reasons  for,  Art.  131, 

mortar  for,  requisites  of,  Art.  132, 

ingredients  with  their  proportions  of,  Art.  133,  134, 

preparation  and  application  of,  Art.  135  to  137,     . 
Pouzzolanas.  meaning  of  the  term,  Art.  54, 

chemical  constitution  of,  Art.  55, 

not  injured  by  exposure,  Art.  55, 

distinguished  into  natural  and  artificial,  Art.  56, 

pouzzolana  proper,  Art.  57,  .... 

substances   comprised   under   the   name   of   artificial, 
Art.  04, 

experiments  with  clays  for  making,  Art.  67,  68,     . 

influence  of  the  contact  of  air  in  the  manufacture  of, 
Art.  69, 

rule  in  the  use  of,  Art.  85, 

manufacture  of  artificial,  Art.  126, 

induration  of,  mixed  with  fat  lime,  Art.  206, 
Prinsep,  Mr.,  his  method  of  analyzing  dolomites,  Art.  24, 
Pumps,  use  of,  in  the  process  of  immersing  beton,  Art.  200, 


Paget. 

82 
83 
83 
84,85 
28 
29 
29 
29 
29 

33 
34,35 

36 
48 
76 

130 
10 

125 


Q. 

Quartz,  impotency  of  caustic  lime  on,  Art.  75, 
Quick  lime,  how  preserved  in  the  large  way,  Art.  41, 


41 
20 


R. 

Rammers,  used  in  "laying"  concrete,  Art.  181,  191,  112,118 

Resistance  of  mortars,  how  estimated,  Art.  92  to  104,  52  to  60 

Roman  cement,  name  applied  to  English,  Art.  42,           .  .         21 

Rueble  masonry,  cost  of,  at  Fort  Warren,  Art.  202,       .  .       127 


S. 

Sands,  different  kinds  of,  how  produced,  Art.  48,  .         .         24 

classification  of,  Art.  49,        ......         24 

choice  of,  for  mortars,  Art.  50, 25 

injured  by  the  presence  of  earthy  matters,  Art.  51,       .         25 
mode  of  cleaning,  in  the  large  way,  Art.  52,         .         .         27 
use  of,  in  mortars,  Art.  53,    ......         23 

that  they  are  inert  substances,  Art.  75,  ...         41 

how  the  voids  of  are  determined,  Art.  76,  77,       .  41,  42 

specific  gravity  of  quartzose,  Art.  77,    ....         42 

object  of  mixing,  Art.  79,  82,         .         .         .         .        42  to  46 

proportions  of,  to  be  used  with   the  different  limes, 

Art.  83  to  87,  46  to  48 

employed  at  Fort  Warren,  Art.  128,  ....  78 
vessel  there  used,  for  determining  voids,  Art.  129,  .  80 
proportion  of,  in  pointing  mortar,  Art.  133,  134,  .         83 


INDEX. 


147 


Pages. 

Sands,  proportion  of,  in  stucco,  Art.  145,        ....         92 
proportion  of,  in  stone  and  brick  mortar,  Art.  160,  161,       101 
Sea  water,  employment  of,  injurious  in  slaking  lime,  Art.  38,         19 
"Set"   or  "setting,"  definition  of,  Art.  13,            ...  5 
quickness  of  set,  indication   of  the  goodness  of  a  ce- 
ment, Art.  19, 8 

Shells,  afford  lime  after  calcination,  Art.  3,  ...  2 

employed  in  making  beton,  Art.  199,  .         .  .       123 

Shrinkage  of  lime,  reason  for  using  sands,  Art.  53,       .         .         23 
reason  for  increasing  proportion  of  cementing  matter, 

Art.  83, 46 

Silica,  its  efficacy  in  a  limestone,  Art.  22,  208,      .         .  10,  132 

Slag  (foundry),  used  as  a  pouzzolana  in  constructing  docks 

at  Sunderland,  Art.  72,       ......         37 

Slaking  of  lime,  defined,  Art.  6,    .....         .  2 

ordinary  process  of,  Art.  32,  34,    ....  15,  16 

expansion  of  bulk  in,  how  ascertained,  Art.  33,  .         16 

second  process  of,  Art.  35,  36,       .....         16 

third  process  of,  Art.  37,  33, 17 

choice  of  the  process  of,  Art.  38,  ....         18 

Sheaton,  his  mode  of  using  pouzzolanas,  Art.  85,  .         .         48 

twenty  different  mortars  used  by,  Art.  90,     ...         51 

his  remark  that  the  hydraulic  property  of  lime  was  due 

to  the  presence  of  clayr,  Art.  208, 

Smith,  Capt.,  mode  of  determining  voids,  Art.  77, 

Solidification  of  mortars,  theory  of,  Art.  203  to  209 

Solubility  of  fat  lime  in  water,  Art.  9, 

Stone,  its  adherence  to  hydraulic  cement,  Art.  103, 

Strength,  comparative,  of  mortars,  how  estimated,  Art.  92 

to  104,        

Stucco,  implements  used  in  laying  on,  Art.  140,   . 
mortar  for  interior,  Art.  141, 
application  of  interior,  Art.  142,  143,    ...  89,  90 

the    employment  of  sugar    or   molasses   advantageous 
when   buildings  are  to    be  stuccoed  with    fat  lime, 

Art.  144,  

for  outside  work  at  Fort  Warren,  Art.  145, 
mode  of  preparing  surface  for,  Art.  146, 
application  of  exterior,  Art.  147,  148, 
on  a  surface  of  concrete,  Art.  149,         .... 
Sugar,   used    to    improve   the   bad   qualities   of   fat   limes, 

Art.  144, 92 

Sulphate  of  lime,  or  plaster  of  Paris,  not  acted  upon  by 

acids,  Art.  27, 12 


123 


131 

42 

to  133 

4 

59 


52  to  60 

88 


Tar,  coal,  used  to  protect  temporarily  the  concrete  roofings 

at  Fort  Warren,  Art.  197, 122 

Trass  or  terras,  composition  and  properties  of,  Art.  58,  .         30 


1/      / 


148  INDEX. 


Fajes. 


Theory  of  the  solidification  of  mortars,  Art.  203  to  209,     128  to  338 
Tiles,  fragments  of,  used  as  an  ingredient  in  making  con- 
crete, Art.  170, 107 

Tile  dust,  used  as  a  pouzzolana,  Art.  70,        ....         36 
Treussart,  Gen.,  mode  of  estimating  the  resistance  of  mor- 
tars, Art.  94,  95, 53, 54 

Totten,  Col.,  mode  of  estimating  the  comparative  hardness 

of  mortars,  Art.  104, 60 

V. 

Vapor,  a  current  of  aqueous,  facilitates  the  reduction  of  lime- 
stone into  lime,  Art.  107,  .....         62 

Vicat,  M.,  table  showing  the  different  rates  of  expansion  of 

the  fat  and  hydraulic  limes  in  slaking,  Art.  38,  .        18 


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